Add continuous integration testing

[khaeru]

This branch adds continuous integration testing using Travis: https://travis-ci.org/transportenergy/database

Steps are required before this can be merged:

• [ ] Supply data for tests. Both the Python and R tests are currently written to use a local copy of the full model database. This is problematic because the data is private, while the code is public. There are at least two options for addressing this:

  1. Using Travis features ([1](), 2) to retrieve a copy of the iTEM data over the Internet for testing, without making it public.
  2. Make up a random/"synthetic" data set on which the tests can operate.

  (ii) is probably easier.

• [x] Fix any other errors in the test script.
• [ ] Merge coverage. There are tools to generate test coverage reports for both Python and R (example), but the coverage reports on subdirectories of this package need to be merged into a single report.

[khaeru]

Per the first TODO, c571408e011a48ea62e5a49e78a345dc6cd54e85 made the Python test suite check whether --local-data was supplied and skip tests that need it.

[khaeru]

• [ ] Supply data for tests. Both the Python and R tests are currently written to use a local copy of the full model database. This is problematic because the data is private, while the code is public. There are at least two options for addressing this:

  1. Using Travis features (1, 2) to retrieve a copy of the iTEM data over the Internet for testing, without making it public.
  2. Make up a random/"synthetic" data set on which the tests can operate.

  (ii) is probably easier.

• [ ] Merge coverage. There are tools to generate test coverage reports for both Python and R (example), but the coverage reports on subdirectories of this package need to be merged into a single report.

These two items can be handled as future enhancements; will merge as-is in order to get continuous integration online.