Added singularity finder for univarite rational functions
Changed to raw strings in LaTeX tests.
Minor formatting updates.
Fixed Interval._eval_imageset

Interval._eval_imageset was not working well the give function was not
monotonic. Now it is evaluated by finding out the maxima, and minima of
the function by solving the derivative of the function in the given
interval.
Added TODO for pretty printing tests.
Merge branch 'master' into issue-2769
Merge pull request #2723 from hargup/imageset

Fixed imageset for Interval
Merge pull request #2772 from moorepants/issue-2769

Fixes issue #2769
Added a init_printing wrapper for simpler time derivative printing.

We like to print f' or \dot{f} for derivatives in
sympy.physics.vector/mechanics. This gives us an init_printing() wrapper to use
inplace of the default one.
Fixed bug that prevented latex rendering.
Removed print statement.
Refactored imports to be consistent.

I moved printing functions/classes into the printing module. Moved the
VectorTypeError into vector. Set mechanics_printing to equal the new
vector.init_printing. Updated doctests to reflect the new behavior. Removed the
time_derivative_printing function in favor of init_printing (no dep warnings
needed, as it was never released, same goes for a lot of this).