Travis buldtest

[Jvinniec]

This is a MASSIVE update. It consists of the following major changes:

• Adds support for downloading UT1-UTC, TT-UT1, and xy polar motion correction values, (issue #13). This means that coordinate conversions are now more accurate. Planet coordinates (in ICRS) computed via the SOFA algorithm are also now more accurate and agree with the AstroPy values to better than a tenth of an arcsecond.
• Adds many new tests for the classes and executables. Many bugs were found and fixed during this process.
• Improves the uniformity and stability of the executables.
• Offloads more of the computation to additional SOFA algorithms.
• Remove the date parameter from CEObserver.

[Jvinniec]

I have now also added changes that I feel resolve issue #10. Specifically, all executables now:

• Use CLOptions class for command line options.
• Use the same parameter names for things like 'ra', 'dec', 'latitude', etc...
• Include the version number and a short description in their help text.