Split physics.mechanics examples into multiple files.
Edited the docstring for ReferenceFrame.orient().
Merge branch 'mechanicsdoc'
Changed title to be consistent with other Physics/Mehcanics titles.
Got bicycle example working by adding a q3 dynamicsymbol.
Gave the rolling disc image a more descriptive file name.
Gave the rolling disc image a more descriptive file name.
Gave the rolling disc image a more descriptive file name.
Updated documentation to reflect change in figure file name.
Got all physics mechanics tests to work again, in part by splitting them into more files.
Got all physics mechanics tests to work again, in part by splitting them into more files.
Add function to return mechanics expressions as strings.
Pyflakes cleanups to matrices
Add table method to Matrix, and modify the string printer

I took this from Chris Smith's work from pull request #1167. I haven't fixed
any of the resulting test failures yet.
Update lambda printer for Matrix
Update doctests with new Matrix printing

I skipped the agca doctests, because the string printer needs to be updated
(it looks silly now), and the mechanics Sphinx doctests, because I think they
really want to be using pretty printing (to get g' instead of Derivative(g(t),
t)).

I haven't yet touched the regular tests.
Fix user_functions argument bug in CCodePrinter
Add test to ccode user_functions argument
Matrix._format_str should be passed a printer, not a function
Update mechanics doctests with updated Matrix printer