Travis: cache pip and compiled libgeos binaries
Travis: cache pip and compiled libgeos binaries

After the cache is built most of the instances will build in less than 2 minutes.  The first time compiling it may take 6-15 minutes per instance.  On "nightly"  libGEOS will always build from source, not sure what pip. It should run about 10 minutes.

Times: [first build](https://travis-ci.org/micahcochran/basemap/builds/98557792) versus [already cached](https://travis-ci.org/micahcochran/basemap/builds/98556050)

Set "middle of the road" configuration to numpy=1.9.3.    A more flexible configuration caused too many problems in testing.  If you know a more maintainable way to do this, please submit a PR.

Cache stored is 670 MiB.

"nightly" will fail until PR #246 is merged.
guziy/basemap,matplotlib/basemap,matplotlib/basemap,guziy/basemap