New Integration class

- Integration class (handles logy/logt/scaling)
- Added new example equilibrium, with test
- Fixed minor bug in cvode_direct
- CHEMREAC_SOLVER_KWARGS picked up by run()
- New analysis convenience function: solver_linear_error_from_integration
- New plotting function: plot_solver_linear_error
- New plotting function: plot_solver_linear_excess_error
- Fixes #12
- Fixes #13
- Use ndarray instead of memory view in wrapper.
- sdist and Docker file to test sdist
- Documentation improvements
- Better test coverage.
- Tweaks for examples