Better support for treating templates and macros as symbols.

This allows you to pass a template or a macro to another macro
which can then inspect the implementation of the former template/macro
using `getImpl`.

Since templates can be freely redefined, this allows you to treat
their symbols as compile-time variables that have lexical scope.
A motivating PoC example for a logging library taking advantage of
this will be provided in the next commit.

Implementation details:

* The name of a template or a macro will be consider a symbol if
  the template/macro requires parameters

* For parameterless templates/macros, you can use `bindSym`, which
  was extended to also work outside of compile-time procs.

compiler/evaltempl.nim

@@ -63,7 +63,7 @@ proc evalTemplateArgs(n: PNode, s: PSym; fromHlo: bool): PNode =
   # if the template has zero arguments, it can be called without ``()``
   # `n` is then a nkSym or something similar
   var totalParams = case n.kind
-    of nkCall, nkInfix, nkPrefix, nkPostfix, nkCommand, nkCallStrLit: n.len-1
+    of nkCallKinds: n.len-1
     else: 0
 
   var