Support terms in patterns with Template Haskell

[fizruk]

Currently patterns can only have patterns, name binders, and non-term data (e.g. labels). Allowing terms in patterns opens up support for the following language features:

• patten type annotations (especially for dependently typed languages, but also see GHC's pattern type signatures in ScopedTypeVariables extension)
• view patterns (see GHC's ViewPatterns extension)
• logical patterns (like pattern matching on _ ++ [x] in Curry)

Technically, I think this is not forbidden by the foil and can be implemented manually, but must be properly handled within the Template Haskell generation functions.