URL-encode Location header (closes #588)

The database returns an array of key-value strings like `"k1=eq.hello
world"`. Haskell URL-encodes the portion after the equal sign and joins
them with `&`.

Includes updates to tests in Feature.InsertSpec: The CompoundPK has been
modified to have one Int and one String. We attempt to add a key with a
String that has spaces and other special characters. This requires that
the returned Location header is properly URL-encoded.

CHANGELOG.md

@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Prevent role from being changed twice - @begriffs
 - Use read-only transaction for read requests - @ruslantalpa
 - Include entities from the same parent table using two different foreign keys - @ruslantalpa
+- Ensure that Location header in 201 response is URL-encoded - @league
 
 ## [0.3.1.1] - 2016-03-28