Add combinators

This so far contains:

* new file `dash-functional.el`
* new file `dash-pkg.el`
* I've moved the combinators from `dash.el` to this new file
* added examples
* moved examples for combinators to the very end (first go list functions, then combinators, it's more logical this way)
* updated the bash scripts to load the new file too.

I can add another commit to this PR that will update the `-max-*` functions or I can do it as separate PR, how do you want it?