makefile: integrate xyz

This cannot be merged as is. The problem is the automatic CHANGELOG generation, which requires knowledge of the new version number. Perhaps [xyz][1] should accept a path to an arbitrary script to be run immediately after the confirmation prompt. This script could be passed the new version number as $1.


[1]: https://github.com/davidchambers/xyz

> ```console
> $ nvm use 0.9
> N/A version is not installed yet
> The command "nvm use 0.9" failed and exited with 1 during .
> Your build has been stopped.
> ```