Issue 3289: substitute warnings for print statements
change print to warning. missing import statement
Merge remote-tracking branch 'upstream/master'
fixed warnings statements in pretty_symbology.py
Fix issue #879: series of undefined functions.
Issue 879: add test for series of a subclass of Function.

Now we can use also

    >>> class TestF(Function):
    ...     pass
    >>> TestF(x).series(x)
Issue 879: fix python3 failure.
Split physics.mechanics examples into multiple files.
Edited the docstring for ReferenceFrame.orient().
Merge branch 'mechanicsdoc'
lxml instead of libxml2 for c2p, google app engine supports lxml and generally better supported
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.
empty line made quality test fail