First attempt at obeying Transient Mark Mode.
Fix docs.
Remove Overwrite code from delete-backward-char.

This assumes there is a prefix, which there is not.

The equivalent of this code in delete-backward-char may be worth
replicating more accurately in this package in the future.
Update docs to talk about Transient Mark Mode.
Do not autoload "iter" functions.
Merge pull request #7 from mwfogleman/transient-mark-mode

Transient mark mode