Version 0.3 changes

These are the major changes to cobrapy for the v0.3. This release should include:
- [x] faster solver interface for pyglpk, gurobi, and cplex with tests
  - [x] change_coefficient
  - [x] change_bounds
  - [x] change objective
- [x] using the faster solver interface for fva and single/double deletions
- [x] cython-based glpk solver
- [x] more flux analysis tools: pFBA and phenotypic phase planes
- [ ] improved documentation
  - [x] new installation instructions
  - [ ] more useage examples
  - [ ] document new solver interface
- [x] expanded unit test coverage
- [x] sbml fbc support
- [x] improvements to ArrayBasedModel
- [x] Simplify API: access read-only attributes
- [ ] integration with zakandrewking/escher@f082b3c875
  - [x] json model export
  - [ ] useage example 
- [x] simplified installation
- [ ] code cleanup
- [x] python 3 support