Fix incorrect emphasis scaladoc markers.

Apparently * doesn’t emphasize, ''' does. Seems legit…
Fix a typo in the Logger docs.
Clarify and improve various scaladocs.

Mostly adding `` around classes and parameters in docs, with
a couple of tweaks to docs that weren’t clear enough.
Bump to Scala 2.11.3.

The specific motivation is that scaladoc in 2.11.3 fixes an
issue with picking up indentation in code blocks properly.
Restore some implicit conversion scaladocs.

These are implicits that take implicits as parameters, and the
docs make it a little clearer what that’s for.