Game string parsing

[Rogueadyn]

• Improve on string parsing (StringHelper class.)

[Rogueadyn]

As of ba3138a:

• Decoder groundwork is ready and should make adding more tags simple.
• Decoding of If, Emphasis, Sheet, Dash and LineBreak tags is fully supported.

[Rogueadyn]

As of f5f439a:

• Added most tags present in game data.
• Unknowns marked with TODO in Text.TagType.