Greatly expand on the Req object

Cut in four different chapters: request, request body,
response and cookies.
erlang.mk now has built-in support for relx
Convert the markdown_middleware example to a release
No need for relx in path for examples anymore
Add relx to the ignore list
Remove the elixir_hello_world example

Elixir examples will be in a separate repository maintained
by Elixir capable developers.
Move cookie parsing/building code to cowlib

The code for parsing has also been rewritten to be more efficient
and to be able to handle cookie values with space inside them properly.

Update cowlib to 0.2.0.
Review, improve and document the static files handler

Changes include:

 *  Much simplified route configuration.

 *  Etag generation is now enabled by default.

 *  Web mimetypes are now detected by default. A bigger list of
    mimetypes can be detected without any additional library.

 *  Mimetypes can no longer be specified as a list. Copying this
    list for new connections is too costy. You can easily convert
    it into a function and pass that function to the handler instead.

 *  You can however specify a single hardcoded mimetype. Mostly
    useful when serving a single file, like an index.html file,
    to avoid extra operations.

 *  Specifying a path as a list of tokens is not possible anymore.
    Use either a binary or a string.

 *  Using a private directory will not work if the application
    was not started properly. Cowboy will not attempt to find
    the location of this directory if the VM doesn't know it,
    as this caused issues in some setups.

 *  Overall the code has been much simplified and clarified,
    and of course has now been documented.
Optimize query string parsing

 *  Parsing code was moved to cowlib: cowboy_qs:parse_qs/1
 *  A function was added to build query strings: cowboy_qs:qs/1
 *  Also added cowboy_qs:urlencode/1 and cowboy_qsurldecode/1
Add link to the repository of elixir Cowboy examples
Add a workaround to disable chunked transfer-encoding

This is an undocumented workaround to disable chunks when using HTTP/1.1.
It can be used when the client advertises itself as HTTP/1.1 despite not
understanding the chunked transfer-encoding.

Usage can be found looking at the test for it. When activated, Cowboy
will still advertise itself as HTTP/1.1, but will send the body the same
way it would if it was HTTP/1.0.
Merge branch 'adrianroe-streaming-http1.1-compat'
Clarify error msg for route lacking starting slash
Merge branch 'dsucher-better-routes-without-start-slash-error'
Use try/catch instead of catch

Thanks Richard Carlsson for the remainder.
Remove an unnecessary clause in cowboy_req:body/2
Properly send 201 on PUT requests when resource didn't exist

Regardless of whether a location header has been set, as explained
in the HTTP RFC.
Update erlang.mk
Update Ranch to 0.9.0
Update ROADMAP