Add automatic-save file #26

As a file is being edited there should be a separate file being saved along side which includes all of the edits. That way if the program crashes or the computer loses power we can resume where we left off. This means checking for that file when opening.

This also allows for a memory purging opportunity. Buffers can direct to part of a file and not yet be loaded (but have a known size). It can point to this shadow file to remove data from memory.

We should research if the file should be along side the original (permissions issue?) or in a separate directory. Make sure the separate directory isn't a temp dir that could be accidentally wiped.