Initial install commit.

What works:
-simple file to file destination install
-multiple files to folder destination install
- -t flag
- partially -m flag, right now accepts mode only on form [ugoa]+[+-=][rwx]+, but in current state should be relatively easy to expand

Any feedback is welcome, some parts of the code are ugly even for me.
Like `show_error!`, this applies throughout the file (other than in `uumain`, where `show_error!` followed by a `return` probably makes more sense).