Added option to presist buffer size on minimap toggle and fixed two typos.

Heyas...

Your version of minimap-mode is cool, but one thing that annoyed me about it was the fact that upon toggling the minimap, your buffer width would be decreased, and there was no option to prevent this from happening for those of us who like to keep our buffers at 80 columns wide.

This pull request adds this option. (And fixes a few minor typos in your documentation and comments.)

You can test the new option out in M-x customize-group "minimap". It is called "Minimap Resizes Buffer".