Add automatic build script and local settings

The script checks for each of the supported solvers, and chooses a default
solver from those that work.

The default solver (and all other settings, but it's the only one right
now) can be accessed via:

from gpkit import settings
settings['defaultsolver']
Tweak build script for Mac
Tweak Mosek version-choosing
Silence CVXopt by default
Remove unnecessary file
Support vector-valued constants
Fix typo
Use spmatrix constructor to take transpose
Specify separate tolerance for each solver
Mosek solver now returns solutions to dual
Make GP sweeps consts looking like ('sweep', vals)
Refactor just about everything; all new nomials

Also began testing variable sensitivities, implemented O(N) substitutions in
GPs, added the ability to load/save cases to GPs, cleaned up the printing
of the examples, and other smaller things.
Add faster var_loc creation on substitution
Add pretty latex printing for iPython & more

Also: constraint checking, example refactoring, and sensitivities
filtering.
Updat examples, Mac mosek_cli compatibility & more
Add python file for pretty printing support
Added Constraints, equality constraints, Models
Rename helpers.py to internal_utils
Add explanatory printing comment
Make GP sweeps consts written as ('sweep', vals)