Change AttributeKey matching to singleton matching

Removes the ClassTag and makes it impossible to generate imposter keys, forcing a one to (one or none) correspondance between key and entry whereas it had been possible to generate "imposter" keys by using the same name and type.
Update comments to reflect the new reality of key equality.
Make EntityDecoder.decode return an EitherT to make DecodingException explicit.
Create type alias for EntityDecode results.
Bring back EntityDecoder.orElse.
Fix broken EntityDecoderSpec.
Merge pull request #84 from http4s/topic/SingletonAttributeKeys

Change AttributeKey matching to singleton matching
Add a few more tests to blaze-server
Don't throw Exceptions, its bad.
Unify DecodingException with ParseFailure. #43
More testing of the entity decoders.
Clean up the Examples

closes #72
ExampleService is cleaned up with the cruft going into a new ScienceExperiments object.
Clean up uri patterns and use 413 status where appropriate.
Merge pull request #97 from http4s/topic/ExampleCleanup

Clean up the Examples
Remove ReplyException. #43 #96

This punts on making errors explicit in the Client: those still get
thrown as a ParseException.

There is a good argument to be made that the apply method added to
EntityDecoder is server DSL syntax, not functionality of the
EntityDecoder.  It also kind of sucks to use an EntityDecoder on the
server without it.
Merge remote-tracking branch 'origin/master' into topic/entity-decoder-eithert

Conflicts:
	blaze-server/src/main/scala/org/http4s/server/blaze/Http1ServerStage.scala
	core/src/main/scala/org/http4s/EntityDecoder.scala
	core/src/main/scala/org/http4s/ReplyException.scala
	examples/src/main/scala/com/example/http4s/ExampleService.scala
	servlet/src/main/scala/org/http4s/servlet/Http4sServlet.scala
Remove rl dependency.

It's unmaintained, which makes it a liability for us for just one
file.  It has served us well, but is `private[util]` so we don't make
any promise to support it oursellves.
Added property that urlDecode(urlEncode(s)) == s.
Update unnecessarily scary comment about 4-byte characters.
Merge pull request #99 from http4s/topic/remove-rl

Remove rl dependency.