Pykep

* Bug fix in equinoctial elements
* New build system

* Updating to pygmo 2 (and dropping PyGMO)
* Adding the Pontryagin module
* Bug fixes on planet ephs (affecting low inclinations and eccentricites)
* Implementation of modified equinoctial parameters
* Adding more examples
* Documentation fixes
* Clang format and pep8 enforced
* Some API improvements (more kwargs)

Several additions were made, notably with respect to the Earth environment.

CI is now uploading binaries to PyPi

It is time for another PyKEP release, this time with **Win64 binaries for Python 2.7 and Python 3.4**!

Changes in this release:
- JPL Spice integration
- Namespace naming changes for `utils` and `planets` to singular form:
- `kep_toolbox::utils` is now `kep_toolbox::util`
- `PyKEP.utils` is now `PyKEP.util`
- `kep_toolbox::planets` is now `kep_toolbox::planet`
- `PyKEP.planets` is now `PyKEP.planet`
- The planet objects have been renamed to reflect the ephemerides type implemented
- Minor bugfixes

**A compatible PyGMO version with this release is 1.1.7!**

Bug fixes
- Epoch cache mechanism updated
- Python3 compatibility improvements