Create TypedTreeMap that propagates types

If some node in tree is transformed changing the type,
the outer node could potentially also change type.

This patch implements a TypedTreeMap that propagates those
changes until types converge. Propagation is done for tree nodes
that are able to compute their type based on their children:
Pair, Block, If, Match, CaseDef, Try, SeqLiteral, Annotated

Note: patch doesn't cover Select's, see #143 for the issue
with Select.
But I think that concern should not be part of RetypingMap. No problem to invoke the TypeAssigner.