script: function get_mk

[Dil3mm4]

Nothing more than a wget on raw content based on treble_generate content

[phhusson]

I'd rather add https://raw.github.com/phhusson/rom_makefiles to manifest
And have build_dakkar inherit vendor/rom_makefiles/${rom}.mk instead of downloading to device/phh/treble/${rom}.mk

As for the concern of destroying dev-s current work, we can either mention this in readme (expected repo way is to repo start vendor/rom_makefiles name-of-my-own-branch, and then the local commits will remain after repo sync-s), or just add a git stash/git stash apply in the build script + ignore git clean -fdx.
I think the repo start way is better, because people will better understand how to work with the rest of the sources. Though this will conflict with apply-patches

[Dil3mm4]

#89