Update PR to include new rules for building slycot from source, which allows proper checking against the slycot version of the library. A couple of notes on the implementation:

• Need to be careful about how to install gfortran and lapack. Install both via apt-get in the root environment (not the test-environment) to make sure that compilers use the right paths (found this out the hard way, but trying almost every other combination of things).

• Python3 implementations need to have the LIBRARY_PATH environment variable set up properly, otherwise slycot will fail to link properly. For this, you need to link to the version in the local environment, so that you get the right version of python.

While I was at it, I made a few other changes:

• Reordered the build cases to start with the most up-to-date case (python-3.6, scipy-1.0, slycot) gets tested version.

• Added more comments throughout to explain what is going on.

• Don't bother to install conda-build since it is not needed any more.

Some of the Travis builds will still fail for this version since the corrections for scipy-1.0 from PR #164 are not yet included.