Initial commit. Migrate from archiso project.

I used to maintain a fork of the archiso project but later
decided that it was more than just about making an iso.
So I created this project and started migrating scripts and docs
over.

Everything in docs/ that ends in *_notes.md is older and incomplete
notes taken directly from my old project.
The only up-to-date doc in there is build.md.
As I convert old docs over they will drop the _notes.md at the end
but for now I'll leave the names as-is so I know which are unfinished.

The scripts build-custom-iso.sh and install-yaourt.sh are up-to-date
but mostly untested.
Next time I install arch on a machine I'll do more testing and
document updating.

I'm also currently debating with myself whether or not to script
out a large portion of the installation/configuration process which
is tedious to do every time I install.

Note that some of the files from root-image in the old project
have been dropped (locale.*, hostname, timezone) but may need to be
re-added.