WIP: Roundtrip Tests

[palday]

A first set of functionality tests.

The foundation for "roundtrip" tests already suggests that there are some floating point / rounding issues -- the last few decimal places don't line up.

Note that these are just a first stab at tests -- the roundtrip tests are nice but slow, so we want more focused tests that we can use to catch errors faster and only have the roundtrip tests as a last line of defense.

To do:

• configure autodownload of sample data when tests are actually run so they aren't distributed with the package
• set up Travis CI
• document sample data