Fix specification to match implementation

As stated in THRIFT-5300, the specification was wrong and type identifiers for collections DO match the field types (except for the obvious boolean type which is then represented as only `BOOL_TRUE`).

Also replaced `BYTE` name with `I8` as the former is documented as a compatibility name only (especially since some languages have an unsigned byte type).

[skip ci] Trivial documentation changes only.
2 files changed