Introduce consistent renaming + some refactoring

[chshersh]

Current naming is not perfect and not consistent. At the beginning I tried to give names according to toml specification. But now I see that it's better to be closer to Haskell. Which brings to the following naming convention:

1. Constructors of Value and ValueType changes to Integer, Text, Double from Int, String, Float. And rename ValueType to TValue.
2. Each parser should have P suffix.
3. Each prism should be capitalised and start with underscore.
4. Each bidirectional converter should be name of constructor without any suffices. When name clashes with Prelude name it should have T suffix (convention for all BiToml configurations).

Also, I want to change module structure a bit to make it more modular:

Split Toml.Types module into Toml.Types.Value, Toml.Types.AnyValue, Toml.Types.TOML, TOML.Types.UValue. This change is also motivated by fact that Toml.Types module becomes very big.

Let me know, what do you think!