Test code examples in docs using doctest

[andyk]

It should be pretty easy to automatically include test example code in our docs via doctest using doctest.testfile on core ReStructuredText files in our docs.

We can also test our demo scripts wherever we end up adding them to the source per #323.

To see how easy it is to us doctest, try out:

# from inside an agentos dev virtualenv
cd agentos
python
>>> import doctest
>>> doctest.testfile("documentation/overview.rst")

**********************************************************************
File "./documentation/repl_quickstart.rst", line 31, in repl_quickstart.rst
Failed example:
    from agentos import Component
Exception raised:
    Traceback (most recent call last):
      File "/opt/homebrew/Caskroom/miniforge/base/envs/tmp_agentos/lib/python3.8/doctest.py", line 1336, in __run
        exec(compile(example.source, filename, "single",
      File "<doctest repl_quickstart.rst[1]>", line 1, in <module>
        from agentos import Component
    ImportError: cannot import name 'Component' from 'agentos' (/Users/andyk/Development/agentos/agentos/__init__.py)
**********************************************************************
File "./documentation/repl_quickstart.rst", line 32, in repl_quickstart.rst
Failed example:
    adder_component = Component.from_class(Adder)
Exception raised:
    Traceback (most recent call last):
      File "/opt/homebrew/Caskroom/miniforge/base/envs/tmp_agentos/lib/python3.8/doctest.py", line 1336, in __run
        exec(compile(example.source, filename, "single",
      File "<doctest repl_quickstart.rst[2]>", line 1, in <module>
        adder_component = Component.from_class(Adder)
    NameError: name 'Component' is not defined
**********************************************************************
File "./documentation/repl_quickstart.rst", line 38, in repl_quickstart.rst
Failed example:
    adder_component.run('add_one', {'Adder':{'add_one':{'x':1}}})
Exception raised:
    Traceback (most recent call last):
      File "/opt/homebrew/Caskroom/miniforge/base/envs/tmp_agentos/lib/python3.8/doctest.py", line 1336, in __run
        exec(compile(example.source, filename, "single",
      File "<doctest repl_quickstart.rst[3]>", line 1, in <module>
        adder_component.run('add_one', {'Adder':{'add_one':{'x':1}}})
    NameError: name 'adder_component' is not defined
**********************************************************************
1 items had failures:
   3 of   4 in repl_quickstart.rst
***Test Failed*** 3 failures.
TestResults(failed=3, attempted=4)