callable - generate template code

[guruofquality]

The template code was always out of hand, it would be nice to generate it:

Notable todos:

• generate for more args then 3 -- howabout 11
• generate wrappers for non const ref args

[guruofquality]

https://github.com/guruofquality/gras/commit/cb0c6da5230aad979153b48d3733984c0d62122e

• didnt do "generate wrappers for non const ref args" -- template ambiguity issues, needs more though