Added Position Support to TomlTree

TomlDocument provides an optional TOML processing path where position
informaiton is stored alongside a TomlTree.
* Added Position struct
* Revised TomlTree to contain position data
* Added tomlValue to bind positions to values
* Revised parser to emit position data
* Revised token to use new Position struct
* Added tests for new functionality
* Bugfixed table array duplicate key handling
* Applied gofmt to all code
Removed redudant license info
Merge pull request #21 from eanderton/master

Element Position Support