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).
Massive cleanup to vector pretty printing.

I didn't know how to use super when I originally wrote this printer,
apparently. Using that makes it way, way cleaner. Also, the new approach is a
little "simpler", but it should be fine in practice.
Removed unicode from doctests.
Excluded vector/__init__.py from wildcard import checks.
Fixed printing issues in doctests.
Updated printing functions api docs.
u'' to u('')/
Cleaned up pretty printing for Vector and Dyadic

More consistent spacing, better sized operators, and proper parenthesis
wrapping.
init_printing > init_vprinting, moved m* print functions into correct module.
Adjusted pretty_print reg tests for new output.
init_printing > init_vprinting
Import print functions in functions.py.
Wrapped warning message.
Simpler command for latex printer choice.
Fixed Python 2.6 string format error.
use warnings and other review edits