Overhaul the semantics of Request.handlerPath and Request.url.

CHANGELOG.md

+## 0.6.0
+
+**Breaking change:** The semantics of `Request.scriptName` and
+[`Request.url`][url] have been overhauled, and the former has been renamed to
+[`Request.handlerPath`][handlerPath]. `handlerPath` is now the root-relative URL
+path to the current handler, while `url`'s path is the relative path from the
+current handler to the requested. The new semantics are easier to describe and
+to understand.
+
+[url]: http://www.dartdocs.org/documentation/shelf/latest/index.html#shelf/shelf.Request@id_url
+[handlerPath]: http://www.dartdocs.org/documentation/shelf/latest/index.html#shelf/shelf.Request@id_handlerPath
+
+Practically speaking, the main difference is that the `/` at the beginning of
+`url`'s path has been moved to the end of `handlerPath`. This makes `url`'s path
+easier to parse using the `path` package.
+
+[`Request.change`][change]'s handling of `handlerPath` and `url` has also
+changed. Instead of taking both parameters separately and requiring that the
+user manually maintain all the associated guarantees, it now takes a single
+`path` parameter. This parameter is the relative path from the current
+`handlerPath` to the next one, and sets both `handlerPath` and `url` on the new
+`Request` accordingly.
+
+[change]: http://www.dartdocs.org/documentation/shelf/latest/index.html#shelf/shelf.Request@id_change
+
 ## 0.5.6
 
 * Fixed `createMiddleware` to only catch errors if `errorHandler` is provided.
 
 * Updated `handleRequest` in `shelf_io` to more gracefully handle errors when
   parsing `HttpRequest`.
 
 ## 0.5.5+1
 
 * Updated `Request.change` to include the original `onHijack` callback if one
@@ skipping 112 matching lines @@
 
 * **BREAKING** Removed `Shelf` prefix from all classes.
 * **BREAKING** `Response` has drastically different constructors.
 * *NEW!* `Response` now accepts a body of either `String` or
   `Stream<List<int>>`.
 * *NEW!* `Response` now exposes `encoding` and `mimeType`.
 
 ## 0.1.0 2014-03-02
 
 * First reviewed release