No longer have py.test run *.rst files

Since py.test cannot see the "testcode/testoutput" blocks inside of our
documentation, making a second run using Sphinx’s "doctest" command
necessary, there is no reason to have py.test look through the *.rst
documentation files.  Even though it might find the occasional Python
prompt example, these will be run by Sphinx anyway during its own test
run.
Add a simple .agignore file
Add RightAscension class plus an explanation of it