fix #1858; Add support for generic templates and macros

Implementation notes:
Just after overload resolution, the resolved generic params will be added to the
call expression to be later processed in evalTemplate and evalMacroCall. These
procs have been modified to handle the increased number of parameters, but one
remaining issue is that immediate templates and macros don't go through the same
process. The next commit will outlaw the use of generic parameters with such macros.

compiler/semcall.nim

@@ -283,8 +283,21 @@ proc semResolvedCall(c: PContext, n: PNode, x: TCandidate): PNode =
     if containsGenericType(result.typ) or x.fauxMatch == tyUnknown:
       result.typ = newTypeS(x.fauxMatch, c)
     return
-  if finalCallee.ast.sons[genericParamsPos].kind != nkEmpty:
-    finalCallee = generateInstance(c, x.calleeSym, x.bindings, n.info)
+  let gp = finalCallee.ast.sons[genericParamsPos]
+  if gp.kind != nkEmpty:
+    if x.calleeSym.kind notin {skMacro, skTemplate}:
+      finalCallee = generateInstance(c, x.calleeSym, x.bindings, n.info)
+    else:
+      # For macros and templates, the resolved generic params
+      # are added as normal params.
+      for s in instantiateGenericParamList(c, gp, x.bindings):
+        case s.kind
+          of skConst:
+            x.call.add s.ast
+          of skType:
+            x.call.add newSymNode(s, n.info)
+          else:
+            internalAssert false
   result = x.call
   instGenericConvertersSons(c, result, x)
   result.sons[0] = newSymNode(finalCallee, result.sons[0].info)