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.

lib/core/macros.nim

@@ -385,7 +385,7 @@ type
 
 {.deprecated: [TBindSymRule: BindSymRule].}
 
-proc bindSym*(ident: string, rule: BindSymRule = brClosed): NimNode {.
+proc bindSym*(ident: static[string], rule: BindSymRule = brClosed): NimNode {.
               magic: "NBindSym", noSideEffect.}
   ## creates a node that binds `ident` to a symbol node. The bound symbol
   ## may be an overloaded symbol.