Move fringe bitmap initialization into minor mode def function.

Also, in turn-on-diff-hl-mode, the all initialization code was inside
(when (window-sytem) ...)
preventing the mode from being enabled at all in a terminal (and not just
the fringe bitmaps from being enabled).
Merge pull request #3 from joseph-churchill/master

Work in terminal and when minor mode function is called directly
Bump the version