Started work on Linearizer Class

Implemented routine for constraints on position and velocity.
Unsure if it will work if either are missing, most likely will need
to add control flow for this. The API is also complicated, and will
be simplified as more code is ported over.

Also added one test for the new linearize routine. Based off of
the example in Luke and Gilbert's paper. As more functionality is
added to the linearization routine, the work done in this test
will get smaller. Still need to add more tests from the examples
I worked out last week.
Lots of work on linearization methods

- Added `to_linearizer` method to KanesMethod class. This returns
an instance of Linearizer with all information needed for the class.

- Made 1 meaninful test with the rolling disc test case. The other
two tests aren't finished yet.

- _subs_keep_derivs was written. This substitutes in values for symbols,
but keeps the derivatives of the from being substituted out.
Assorted fixes in Linearizer Class

- Forgot to multiply A and B by P^T when outputting just the
A and B matrices. Fixed.

- Added an eigenvalues test in the rollingdisc test

- Formatting and code quality fixes
Added support for no f_c/f_v in Linearizer

The Linearizer class now supports linearization for systems with
 - Both configuration and motion constraints
 - Only configuration constraints
 - Only velocity constraints
 - No constraints

Added a test for no constraints. Still need tests for just f_c and
just f_v. Added rough beginnings of `linearize` class method for
KanesMethod. The interface still needs to be decided on.
Generalized Linearization Routine

The following changes were made to the Linearizer Class:

1.) Now accepts if q, u, or any of the f_# generalized terms
are empty matrices. Linearization proceeds as it should.

2.) Broke the linearization process into a couple "private"
class methods. The ones done so far only need to be run once
upon initialization. This should save calculation time if the
user intends to do multiple linearizations about different
operating points.
Changes to Linearizer and Related tests

- All tests now are valid and pass
- Improved doc strings, still needs more work
- Modified tests for KanesMethod to use the new functionality

Now have the same functionality as before with linearizing
KanesMethod objects, but code is more generalized and easily
extended.
The latest version of livereload does not use the -b option
Move the printing part of the tutorial after the gotchas and basic operations

Pretty printing is not used in the tutorial until after these sections, and
they are more important than printing.
Include simplification
Don't use bullets for the "whet your appetite" section

It just looks bad.
Wording
Note that the printing options are in the settings (which are hidden by default)
Some wording on the "Why SymPy?" section
Spell functions as function() in the printing tutorial
Don't use `` in section titles in the simplification part of the tutorial
Write functions as function() in the simplification section of the tutorial

I have used the convention that Python functions are written as function(),
but SymPy objects (like sin) are not.
Grammar
Code cleanup, pep8 fixes, docstrings edits

- Code cleanup with flake8 for pep8 fixes in new code
- Edits to docstrings
- Fixed doc tests
Fix for python 2.6 - dict comprehension changed

Using a generator expression and the dict() constructor now.
Docstring fixes, and small bug fix

- Fixed the docstring issues found in code review.
- Also, M_uqd = f_3.jacobian(qd), not f_2.jacobian(qd) as was
written previously.