update some docs (valhalla#4002)

* update build instructions for linux

* update contributing docs C++ version

CONTRIBUTING.md

@@ -9,7 +9,7 @@ There are many ways to make meaningful contributions to the project:
 ## Code contributions
 
 We appreciate the community picking up and fixing bugs or even implementing new features. There are a few things to follow/be aware of when working on Valhalla:
-- we currently use the C++14 standard
+- we currently use the C++17 standard
 - we use `pre-commit` to make sure commits are formatted & linted: run `./scripts/format.sh` once and it'll be installed
 - `clang-format`/`clang-tidy` is used to format/lint the C++ code, `black` & `flake8` format/lint Python code
 - [`ASan`](https://clang.llvm.org/docs/AddressSanitizer.html) is run in CI, but without its integrated leak sanitizer due to platform issues

docs/docs/building.md

@@ -38,15 +38,7 @@ cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_OSX_ARCHITECTURES="x86_64"
 To install on a Debian or Ubuntu system you need to install its dependencies with:
 
 ```bash
-sudo add-apt-repository -y ppa:valhalla-core/valhalla
-sudo apt-get update
-sudo apt-get install -y cmake make libtool pkg-config g++ gcc curl unzip jq lcov protobuf-compiler vim-common locales libcurl4-openssl-dev zlib1g-dev liblz4-dev libprime-server-dev libprotobuf-dev prime-server-bin
-#if you plan to compile with data building support, see below for more info
-sudo apt-get install -y libgeos-dev libgeos++-dev libluajit-5.1-dev libspatialite-dev libsqlite3-dev wget sqlite3 spatialite-bin python3-shapely
-source /etc/lsb-release
-if [[ $(python3 -c "print(int($DISTRIB_RELEASE > 15))") > 0 ]]; then sudo apt-get install -y libsqlite3-mod-spatialite; fi
-#if you plan to compile with python bindings, see below for more info
-sudo apt-get install -y python-all-dev
+./scripts/install-linux-deps.sh
 ```
 
 Now you can build and install Valhalla, e.g.