Added the ability to get the previous workday by passing in a negative
number of days along with the date to start from.
This update also includes some overhauling to allow for the library to
be more resilient to changes in the upstream API.
* feat: pull country or language by code.
This differs from the existing `search` functionality in that it allows
you to explicitly pull back a single country or language instead of
anything that matches (which could result in more items returned than
expected).
* docs(readme): update to include examples for new functionality.
* test: expand tests to include new parameters.
* fix(client): dropped some commented out code that wasn't in use.
* docs(license): bump the year of the license.
* Reworked interfacing to drop the versioning in the class name.
* Refactored / cleaned up existing code.
* Stuck with support for PHP 5.3+ since PHP 5.x still seems to hold majority.
* Abstracted request logic to another class for mocking.
* Added test suite and hit full code coverage.
* Updated readme, included migration guide and the full gamut of examples.
* Wired up travis-ci and coveralls for testing and coverage.
