Log Message:
editors: Add neovim. Based on the pkgsrc-wip package (although
with an update, lots of changes, and unncessary stuff removed).

Thanks to Claes Nästén, snow flurry, kamil, and others.

Neovim is a project that seeks to aggressively refactor the "Vim"
text editor in order to:

* Simplify maintenance and encourage contributions
* Split the work between multiple developers
* Enable advanced UIs without modifications to the core
* Maximize extensibility