Npgsqltypes files refactor

There should be no functional changes in this commit.
Split NpgsqlTypesHelper.cs and NpgsqlTypeConverters.cs into more managable pieces.
Move class ASCIIByteArrays{} to ASCIIBytes.cs.
Move unused messages under NpgsqlTypesHelper.cs to Messages.cs.
Changed file encoding (removed unneeded BOM, it's just ASCII) and copyright date on FastConverter.cs.
Remove Messages.*, as the strings are not used at all anymore.
Merge pull request #66 from glenebob/npgsqltypes_files_refactor_3

Npgsqltypes files refactor