Fix encoding of the LOCAL_ONE consistency level.

It seems to have been an error in the spec. See https://github.com/apache/cassandra/commit/09c7dee2554f6732505e603b16127a2c0b426d49
Merge pull request #1 from romanb/fix-local-one-consistency

Fix encoding of the LOCAL_ONE consistency level.
Fix codec issue w.r.t. `varint`.

Also move over relevant tests from `cql-test` repository.
Ensure GHC 7.8 compatibility.
Add support for column-type 'text'.

Also replace `CqlVarChar` with `CqlText` and make column-type
checking accept mixed `VarCharColumn` and `TextColumn` types.
Remove copy of CQL spec