documented static params
make the current PContext accessible through TCandidate

the goal here is to remove all the hacks from ParamTypeMatch and to handle
all type matching in typeRel (the context there is required to evaluate any static
params and to run the compilation tests of user-defined type classes)
wip type class reforms (the compiler bootstraps fine)

* replace tfAny and tfAll with tyAnd and tyOr
* integrate matchTypeClass into typeRel
* introduce tyBuiltInTypeClass to handle types such as tuple, object, proc, etc
better integration of tyStatic into typeRel
test case for semistatic
bugfix: in some contexts, newSeq[T](n) is incorrectly inferred to have a seq[typedesc[T]] type