[#19] Properly hides data types, and exposes the content of Toml.Table.Key.

Also exposes Toml.Equal for the tests.
Removes useless test.
Fixes typos in documentation.
Adds convenience function to build a key.
[#21] Prints 'round' floats (eg, 1.0) correctly.
Compare module instead of Equal module.
Adds _build and toml.docdir to gitignore.
Adds .merlin file.
Merge pull request #20 from Emm/v2_abstract_types

V2 abstract types