Automatically call batch.sh commands when filea re missing (matteor/auto-patcher#74)

This is meant to fix mateor/auto-patcher#74 by doing the following:

1. Move the `batch.sh` commands into a function in `auto_patcher`, `prep_patches`.
2. In batch.sh, remove duplicating `expath` and `abspath` functions and just source `auto_patcher` directly.
3. Make `batch.sh` just call the `prep_patches` function from the source auto_patcher file.