plumbs prettyprinting of `def foo(x_ : Bar) = ???` (pending a thorough fix)
prettyprinting fix for associativity of infix extractors
plumbs parenthesization of non-operator expressions

This is something that has already been started with fixes to how
assignments and ascriptions should be parethesized, but reality is much
richer than I've imagined.
Merge pull request #41 from xeno-by/master

a bunch of hotfixes to advance the prototype of scalahost