provide a way for unapply macro to obtain a list of subpattens

This commit introduces internal attachment that allows unapply macros to
be aware of their sub patterns and tweak their expansion depending
on that info.

At the moment this is not possible due to the way pattern macros are
expanded:

	case MacroPat(inner1, inner2) => ...

During type checking this will expand as

	MacroPat.unapply(<unapply-dummy>)

Meaning that macro can’t see inner1 and inner2 in it’s macroApplication.
To circumvent this we attach that info as an attachment to the dummy.

Refactor holes, move liftable into the cake and introduce unliftalble

1. Refactor Holes slice of quasiquotes to make unliftable fit into
   the same framework; replace 3 entities: Holes, HoleTypes and Location
   with just a single Hole concept (equiv to previous Holes + HoleTypes)
   and some matchers over types (equiv to previous Locations);

2. Move Liftable trait inside of the cake; this is crucial to decrease
   boilerplate that is required to define liftable and to allow
   combining of liftables together with unliftables in the same class
   without pulling ones hair out;

3. Introduce Unliftable — a type class similar to liftable that lets
   users to extract custom data types out of trees with the help of
   straightforward type ascription syntax:

      val q“foo.bar(${baz: Baz})” = ...

   This will use Unliftable[Baz] to extract custom data type Baz out of
   a tree nested inside of the another tree. A simpler example would be
   extracting of constant values:

      val q”${x: Int} + ${y: Int}” = q”1 + 2”

4. Vastly increase number of standard liftables.

fix unlift

hide liftables away from top-level of the cake

let liftables be defined in public api