Fixed my name in CONTRIBUTORS file.
Added support for unique and index on MySQL. It also adds supports for compound unique and compound index by using special variables __mamba_unique__ and __mamba_index__.
Unique keys are created first as this is good for MySQL internal optimization engine.
Added single and compound index/unique creation for Postgres. Fixed a few bugs on MySQL one. Made naming more consistent.
Added support to single and compound unique/index on SQLite.
Update docs.
Merge pull request #23 from nicholasamorim/index_and_null_support

Index and unique support, resolves #18