Get python bindings via nanobind, seemingly working.

Tested on macOS - and everything now seems reasonable.
But I'm sure there will be a number of changes needed.

bindings/python/CMakeLists.txt

@@ -14,10 +14,9 @@ set( SpecUtils_FLT_PARSE_METHOD "strtod" CACHE STRING "Float parsing method" )
 add_subdirectory( ${CMAKE_CURRENT_SOURCE_DIR}/../.. ${CMAKE_CURRENT_BINARY_DIR}/LibSpecUtils )
 
 if (NOT SKBUILD)
-  message(WARNING "\
-  This CMake file is meant to be executed using 'scikit-build'. Running
-  it directly will almost certainly not produce the desired result. If
-  you are a user trying to install this package, please use the command
+  message(FATAL_ERROR "\
+  This CMake file is must be executed using 'scikit-build'. 
+  If you are a user trying to install this package, please use the command
   below, which will install all necessary build dependencies, compile
   the package in an isolated environment, and then install it.
   =====================================================================
@@ -28,7 +27,7 @@ if (NOT SKBUILD)
   in your environment once and use the following command that avoids
   a costly creation of a new virtual environment at every compilation:
   =====================================================================
-   $ pip install nanobind scikit-build-core[pyproject]
+   $ pip install nanobind scikit-build-core
    $ pip install --no-build-isolation -ve .
   =====================================================================
   You may optionally add -Ceditable.rebuild=true to auto-rebuild when

bindings/python/README.md

@@ -1,76 +1,27 @@
-Instructions to build and install a python wheel file.
+# Python bindings to SpecUtils
 
-It could be more automated, or polished, or whatever, but this works.
+[nanobind](https://github.com/wjakob/nanobind) is used to create the Python bindings to SpecUtils.
 
 
-## macOS build instructions 
-Tested on M1 on Ventura, with Xcode 15.1
-```bash
-# Setup deployment target and path where you will install boost
-export MACOSX_DEPLOYMENT_TARGET=10.13
-export MY_BOOST_PREFIX=/path/to/install/prefix/to/macOS_boost_1_85_prefix
-
-
-# Download and build boost with Python support (any non-ancient version of boost should work)
-cd /tmp/
-curl -L https://boostorg.jfrog.io/artifactory/main/release/1.85.0/source/boost_1_85_0.tar.gz -o boost_1_85_0.tar.gz
-tar -xzvf boost_1_85_0.tar.gz
-cd boost_1_85_0
-
-# build the b2 executable
-./bootstrap.sh cxxflags="--arch arm64 -mmacosx-version-min=10.13" cflags="-arch arm64 -mmacosx-version-min=10.13" linkflags="-arch arm64 -mmacosx-version-min=10.13" --prefix=${MY_BOOST_PREFIX}
-
-# point boost to the Python install we want to use, by using a user-config.jam file
-#  Here I'm using the brew install of python 3.11
-echo "using python : 3.11.6 : /opt/homebrew/opt/python3/bin/python3 : /opt/homebrew/opt/python3/Frameworks/Python.framework/Versions/3.11/include/python3.11/ : /opt/homebrew/opt/python3/Frameworks/Python.framework/Versions/3.11/lib/libpython3.11.dylib ;" > user-config.jam
-
-# build and install boost for arm64 - we will only make static libs, so this way the 
-#  final SpecUtils module library will be self contained.
-./b2 --user-config=./user-config.jam toolset=clang-darwin target-os=darwin architecture=arm abi=aapcs cxxflags="-stdlib=libc++ -arch arm64 -std=c++14 -mmacosx-version-min=10.13" cflags="-arch arm64  -mmacosx-version-min=10.13" linkflags="-stdlib=libc++ -arch arm64 -std=c++14 -mmacosx-version-min=10.13" link=static variant=release threading=multi --build-dir=macOS_arm64_build --prefix=${MY_BOOST_PREFIX} -a install
-
-# remove the boost src and build files
-cd ..
-rm -r boost_1_85_0.tar.gz boost_1_85_0
-
-# build SpecUtils
-cd /path/to/SpecUtils
-mkdir build_python
-cd build_python
-cmake -DSpecUtils_PYTHON_BINDINGS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_OSX_DEPLOYMENT_TARGET="10.13" -DCMAKE_PREFIX_PATH=${MY_BOOST_PREFIX} -DCMAKE_BUILD_TYPE=Release -DCMAKE_OSX_ARCHITECTURES="arm64" ..
-cmake --build . --config Release -j10
-
-
-# now, lets test it
-mkdir pytest
-cd pytest
-# We need to rename the shared library to something that will work with Python
-cp ../libSpecUtils.dylib ./SpecUtils.so
-cp ../../bindings/python/test_python.py .
-# The `test_python.py` script uses the `passthrough.n42` file from InterSpec, so
-# we need to copy that into the current directory
-cp /path/to/InterSpec/example_spectra/passthrough.n42 .
-
-# Now run the test script, making sure to use the same Python we compiled boost against
-/opt/homebrew/opt/python3/bin/python3 test_python.py
-# You should see some output
-
-
-# if you want, you can create a proper package (although these instructions may be out of date)
-mkdir SpecUtils
-cp ../bindings/python/__init__.py ./SpecUtils/
-cp libSpecUtils.dylib ./SpecUtils/SpecUtils.so
-ln -s ../bindings/python/setup.py .
-python3 setup.py bdist_wheel
-python3 -m pip install --user --force dist/SpecUtils-0.0.1-cp39-cp39-macosx_12_0_x86_64.whl
+To compile the bindings, run the following commands:
+```
+mkdir my_venv
+python3 -m venv my_venv
+source my_venv/bin/activate
+cd my_venv
+pip install /path/to/SpecUtils/bindings/python
 ```
 
-## Windows build instructions
-Assumes you already compiled boost with Python support. The script `get-boost.ps1` will help you with this.
-
-Run these powershell scripts to build SpecUtils with python bindings and install the bindings into your python environment. Tested with python 3.11.
+To run the examples, run the following commands:
+```
+cd examples
+python test_python.py
+python make_file_example.py
+python make_html_plot.py /some/path/to/a/file.n42
+```
 
-```ps1
-# Run these in a Visual Studio Development Powershell Console
-PS C:\Projects\code\SpecUtils\bindings\python> .\build-4-python.ps1
-PS C:\Projects\code\SpecUtils\bindings\python> .\make-wheel.ps1
+To run the tests, run the following commands:
 ```
+python -m unittest tests/test_specutils.py
+```
+