Providing support for (mod:func ...) calls

This change will allow LFE programmers to make calls to Erlang using the same syntax they do in Erlang itself. Here's some example usage from the REPL:
### Usage
```cl
> (orddict:new)
()
> (string:tokens '"apple:seed" '":")
("apple" "seed")
```
Note that the old form continues to work (and is more efficient, since it involves fewer function calls):
```cl
> (: orddict new)
()
> (: string tokens '"apple:seed" '":")
("apple" "seed")
```
Other operations still function as expected:
```cl
> (+ 1 2 3 4 5 6)
21
> (* 2 (+ 1 2 3 4 5 6))
42
```
### Implementation Details

A new ``exp_predef`` function was added to ``lfe_macro.erl``. This was placed next-to-last of the ``exp_predef`` functions (any earlier, and it would have interfered with other ``exp_predef``s).