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.
Clarify error msg for route lacking starting slash

[Finishes #491]