Add api module that contains the public interface of the package.
Add api module that contains the public interface of the package.

The methods are categorized as follows:

* New: Create brand new ULID instance from nothing.
* Existing: Create entire ULID instance from 128 bits
of bytes, int, str values.
* Partial: Create part of a ULID instance from existing
timestamp or randomness values.

ahawker/ulid