allow keyword params for the [] and {} operators

conceptually, these operators are not very different from regular procs in the way
they are defined and overloaded. keyword params for them are admittedly less useful,
but they improve consistency and may help with generic instantiations once default
generic parameters are supported.

compiler/parser.nim

@@ -627,6 +627,13 @@ proc identOrLiteral(p: var TParser, mode: TPrimaryMode): PNode =
     getTok(p)  # we must consume a token here to prevend endless loops!
     result = ast.emptyNode
 
+proc namedParams(p: var TParser, callee: PNode,
+                 kind: TNodeKind, endTok: TTokType): PNode =
+  let a = callee
+  result = newNodeP(kind, p)
+  addSon(result, a)
+  exprColonEqExprListAux(p, endTok, result)
+
 proc primarySuffix(p: var TParser, r: PNode): PNode =
   #| primarySuffix = '(' (exprColonEqExpr comma?)* ')' doBlocks?
   #|               | doBlocks
@@ -636,11 +643,8 @@ proc primarySuffix(p: var TParser, r: PNode): PNode =
   result = r
   while p.tok.indent < 0:
     case p.tok.tokType
-    of tkParLe: 
-      var a = result
-      result = newNodeP(nkCall, p)
-      addSon(result, a)
-      exprColonEqExprListAux(p, tkParRi, result)
+    of tkParLe:
+      result = namedParams(p, result, nkCall, tkParRi)
       if result.len > 1 and result.sons[1].kind == nkExprColonExpr:
         result.kind = nkObjConstr
       else:
@@ -653,10 +657,10 @@ proc primarySuffix(p: var TParser, r: PNode): PNode =
     of tkDot:
       result = dotExpr(p, result)
       result = parseGStrLit(p, result)
-    of tkBracketLe: 
-      result = indexExprList(p, result, nkBracketExpr, tkBracketRi)
+    of tkBracketLe:
+      result = namedParams(p, result, nkBracketExpr, tkBracketRi)
     of tkCurlyLe:
-      result = indexExprList(p, result, nkCurlyExpr, tkCurlyRi)
+      result = namedParams(p, result, nkCurlyExpr, tkCurlyRi)
     else: break
 
 proc primary(p: var TParser, mode: TPrimaryMode): PNode