Update docs for 1.2a release

Labeling this one as "alpha" because it is still pretty rough
and raw, but seeing as the code is on the master branch and
most people are following master (due to the way the Vim
plug-in ecosystem operates), may as well draw a line in the
sand to say this is close to what I want to "release".

doc/ferret.txt

@@ -590,10 +590,11 @@ order):
 
 HISTORY                                                        *ferret-history*
 
-next (not yet released)
+1.2a (16 May 2016)
 
 - Add optional support for running searches asynchronously using Vim's |+job|
-  feature; see |g:FerretJob|, |:FerretCancelAsync| and |:FerretPullAsync|.
+  feature (enabled by default in sufficiently recent versions of Vim); see
+  |g:FerretJob|, |:FerretCancelAsync| and |:FerretPullAsync|.
 
 1.1.1 (7 March 2016)