fix misspelling in documentation conf.py

mathjax cdn url was not being set to https because of this.
DOC: add faq and bugfixes

Add an FAQ notebook to answer common questions. It now answeres the
question of how to rename reactions/metabolites, which fixes #78.

The QP example now also has figures to better illustrate the problems.
cglpk: add function to write problem to LP file
quadratic_component is an optional keyeword arg

No longer pass quadratic_component=None to all solvers by default and
force them to implement code to ignore it if they do not support
quadratic programming. When specified, it is still passed on.
cglpk: bugfix to LP file writing with python 3
Add exact solving to cglpk

This is controlled by the exact=True parameter. However, this requires
an additional dependency on libgmp (which can also be statically
linked).
add bindings to QSopt_ex aka esolver

The solver uses cglpk to construct the problem and write out an LP, and
the command line interface to esolver is used to solve it. Esolver can
use rational math to solve an LP exactly.
test esolver on travis
Merge pull request #126 from aebrahim/exact

Add exact solving to cobrapy
cglpk.write_lp is now write and also does mps

The format is detected from the file extension.
Saving gene names in JSON files; specified default JSON dump params.

Specifically, allow_nan=False.
Merge pull request #127 from zakandrewking/master

Save genes in JSON and mat files, and options for JSON export.
Parse formula containing floating point values

A warning is still raised when floats are encountered, but this does not
prevent parsing of the composition.

This fixes #128
Support for the MOSEK solver

For now, this only will solve linear programs with Python 2. Support for
MILP, QP, and Python 3 should be added in a future commit.
io.read_legacy_sbml wrapper uses old_sbml=True
support for MILP and QP in mosek

Also add an additional test for MILP unit testing to ensure the solution
status if 'feasible' for a feasible model.
small fix to reaction display

This will allow symbolic stoichiometry to render in the reaction,
provided that the value has a sign specified. For example,

```python
import cobra.test
from sympy import Symbol
m = cobra.test.create_test_model()
x = Symbol("x", positive=True)
m.reactions.PGI._metabolites[m.metabolites.f6p_c] = x/2
m.reactions.PGI.reaction
```
will output
```g6p_c <=> x/2 f6p_c```
all of cobra core passes pep8

This is mostly whitespace and other small changes, such as rearranging
unnecessary list comprehensions to loops.