Pykep

This release contains the modifications that were deemed necessary to integrate pykep into the ESA "Optimize" platform!
We also thank pabloem for adding linting to the CI thus catching early on possible python issues.

As revealed by conda's toolchsin, the cspice code definition of the complex type is in conflict with win compiler. This point release fixes the issue changing that name to complex_type.

* The new cSPICE version is N0066, released April 10, 2017 from JPL.
* Several small bug fixes. All jupyter notebooks now run.
* Doc improvements

In this release we have heavily reworked the build system as well as introduced a few interesting features, namely:

1 - A more, consolidated, prototype for the interplanetary trajectory gym.
2 - The possibility to compute complex gravity accelerations (due to high order harmonics).

Docs have been improved, but that is an area were more

This release includes general bug fixes and improvements. In particular equinoctial elements conventions are changed and TLE reads are now compatible with py27-37.

In this release:

New Features
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* The start of the open traj gym project. First few problems are added
* Build system Update
* Python 37 binaries

Bug FIxes
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* Update to pygmo 2.7 so that examples work (73 )