typedesc and expr params

types are now valid proc/template/macro params and you can overload over them:
proc foo(T: typedesc)        # accept any type
proc foo(T: typedesc{int}) # overload specifically for int
proc foo(T: typedesc{int or float or Callable}) # overload for any type matching the constraints

expr{type} is a param expecting compile time value of the designated type (or type class).

when typedesc or expr params are used with a proc, the proc will be instantiated once
for each unique type/value used as parameter.

compiler/sem.nim

@@ -91,7 +91,7 @@ proc semConstExpr(c: PContext, n: PNode): PNode =
 
 proc semAndEvalConstExpr(c: PContext, n: PNode): PNode = 
   result = semConstExpr(c, n)
-  
+
 include seminst, semcall
 
 proc semAfterMacroCall(c: PContext, n: PNode, s: PSym): PNode =