Add PHPUnit test framework

See #52
Add tests for exporting methods

See #52, #121
Add .travis.yml

See #52
Travis CI: install dependencies

See #52
Move method use tests and improve docs

See #52
Fix PHP 5.3 syntax error
Make $export_data non-static

Otherwise it persists between tests.
Merge pull request #122 from JDGrimes/issue-52

Sample unit tests with PHPUnit