Remove columns from Relation
Put type of what into Select type parameters
Add fetchAll and fetchOne in executor syntax
Add scaladoc to HListExtractor
Change HListExtractor to take HList of Extractors - implement it
Rename fetch methods
Define `AliasedColumns` and `Extractable` typeclasses to allow shapeless to be removed
Rename toSeq to columns
Merge branch 'select-columns'

Conflicts:
	core/src/test/scala/sqlest/sql/BaseStatementBuilderSpec.scala
	project/Build.scala