Add =exec-path-from-shell= through el-get

This library is useful to manage environment variables on osx. This
solves long-standing problems about correctly loading the path.
Upgrade =elpy= from upstream

The latest version (v1.5.0) removes dependency on auto-complete, and
brings a lot of important improvements.

Modify README with new instructions for =elpy=
Fix: value for =company-idle-delay= has changed.
Follow elpy's convention for jumping to flymake errors

Basically, =C-c C-n= for =flymake-goto-next-error= and =C-c C-p= for
=flymake-goto-prev-error=
Add support for golang programming.

Feel free to go nuts.
Remove my copy of the fixed go-company recipe

The changes were merged upstream into
el-get. (https://github.com/dimitri/el-get/pull/1852)