Replace mxGetPr

[lfarv]

As reported by @carmignani in #52, Matlab R2018a introduces a new C API where:

1. The representation of complex variables is changed (interleaved real and imaginary parts instead of separate real and imaginary arrays (no problem for AT : no complex data accessible in integrators)
2. Data access should be done with specialized macros (mxGetDoubles, mxGetInt32s...) instead of mxGetPr

This new API is accessed when using the -R2018a flag in the mex command. This not the default yet but it will come in the future. The proposed modifications apply the new API when the -R2018a flag is used and keep the old one otherwise, as for the previous Matlab versions.

While doing this, all integrators have been converted to the Python-compatible trackFunction instead of passFunction

[willrogers]

Looks fine to me, and the tests still pass.

[carmignani]

It looks very good!

[lfarv]

When converting the few last integrators to the trackFunction, I found some problems with data-ordering: see #56. Until this is solved, I think that in pyat:

• the processing of axis rotations is wrong.
• Matrix66Pass and MatrixTijkPass are wrong