APE1 tweaks

Mostly small tweaks I noticed that were easier done by hand than suggesting them in astropy/astropy-APEs#1

Two changes of significance:

* I changed "Standards Track" to "Standard Track" because it seems like it makes more sense for us.
* I added an "APE Status" section that describes the various options with explanations for how to get to those steps.  If this looks good, I'll tweak the APE template directly in master to mention that the "Decision rationale" should be done after merging.