Add full-text search/tsvector functions and types

[mrkgnao]

@k0001 what would need to be done to implement this? I really need this feature for my own work, so I'm prepared to put in some work (which it seems will have to start from postgresql-simple 😨)

[k0001]

Thanks for your interest!

Some things I can think of off the top of my head:

1. We need data PGTsVector and data PGTsQuery to be used as type level indexes for database side stuff, both with PgPrimType and PgTyped instances.

2. We need to introduce data TsVector = ... and data TsQuery = ... for correctly representing tsvector and tsquery in Haskell (probably in Tisch.Internal.Kol).

3. We need ToKol instances for TsVector and TsQuery.

4. We need to add functions that work on Kol TsVector and Kol TsQuery to Tisch.Internal.Fun.

[mrkgnao]

So will all the work be in Tisch? I understand you're planning to remove the Opaleye dependency, but postgresql-simple doesn't support tsvector/tsquery, it seems.

I think the TsVector and TsQuery types should be newtyped Map Lexeme Weight, where

data Lexeme = Lexeme { unLexeme :: Text }
data Weight = Weight Int Priority
data Priority = PrioA | PrioB | PrioC | PrioD