POSTing a String via <<(String) defaults to UTF-8 encoded "text/plain"

- adds setBodyEncoding(charset: String)
- adds setContentType(mediaType: String, charset: String)
- <<(String) defaults to text/plain; charset=UTF-8
setContentType sets body encoding too
Merge branch 'topic/uft8body' of github.com:eed3si9n/reboot

Conflicts:
	core/src/main/scala/requests.scala
upgrade to sbt 0.13.1
Some build changes we'll need for 2.11.

This still won't build 2.11.0-RC4 as is, because ufcheck depends on
scalacheck and that build is only compatible with some different
pre-release version of 2.11.
pick a scalacheck hash that works with scala 2.11.0 final
remove what I think is an unnecessary and confusing build instruction,
but maybe I will regret this
broaden access scope of this method, as scala 2.11 apparently requires
freshen up these versions
scalacheck is really nicely crosscompiled these days so we can stop
these source dependency shenanigans that require unfathomable
adjustments after some sbt upgrades
oh cool another sbt upgrade
update json4s-* lib deps
Do not duplicate query on segment addition
scala 2.11 compatibile dependencies
Merge pull request #80 from skazhy/duplicate_query

Do not duplicate request query on segment addition
upgrade from async client v1.7.19 to latest (1.8.8)
Recognize when running in sbt 0.13.1+

Note: side effect of the 1.8.8 client upgrade is that the console is
not exited cleanly even if sbt is detected. Probably some new
threadpools need to be shutdown.
ahc has added a timer, so configure it to use ours when running inside sbt
addresss sbt warning
respond to scalacheck deprecations