remove karta from requirements because it's not in pypi right now
handle failure to import scipy

Calling functions that rely on scipy will result in an error. These tend to be
specialty modules, and don't include core functionality.
raise CRSError if trying a lon-lat azimuth without pyproj
Verify that the source files for extension modules in place, and if not, abort building extensions
Merge branch 'travis'
add build indicator and get travis deps via apt
fix typo in .travis.yml
update dependency lists
experimenting with travel YML

trying to prevent travis from recompiling cython/numpy from source