Add simplify.simplify() function.
Add simplify.simplify() function.

It's just a convenience wrapper around using the ConditionalsSimplifier
class.  It can be used e.g. to report boolean expressions nicely in
later stages of processing, when some parts (e.g. toolset tests) can be
removed.

vslavik/bakefile,vslavik/bakefile,vslavik/bakefile