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Merge branch 'eanderton-master'
Fixes #20 : Creation of subgroup in table arrays
Add 1.3 to Travis' build matrix
Added Position and Document support

TomlDocument provides an optional TOML processing path where position
informaiton is stored alongside a TomlTree.
* Added Position struct
* Added TomlDocument struct
* Revised parser to emit position data
* Revised LoadFile() and Load() to use revised parser
* Revised token to use new Position struct
* Added tests for new functionality