Remove cowboy_dispatcher

Types and code are moved to cowboy_router. The match/3 export
from cowboy_dispatcher isn't available anymore as it is called
internally.
Update handler callback specs

There is one another {upgrade, ...} quintuple allowed as the result of
Handler:init call, somewhy not mentioned in the callback specifications.
New routing

Ultimately few things change, it's mostly just a nicer syntax and
slightly different expectations. The name of the value `dispatch`
did not change, because the previous dispatch values will now fail
if the code is not updated to using `cowboy_router:compile/1`.

No constraints have been implemented in this commit.
Add the 'int' constraint
Add the 'function' constraint
If a binding is reused, we check that values are identical

This is more for consistency than anything.
Update roadmap
Update Ranch to 0.6.1
Makefile: only recompile files newer than the .app
Merge branch 'fix/callback_specs' of https://github.com/keynslug/cowboy
Add a section about closing the connection in the guide
Do not attempt to skip the request body on Connection: close
Fix {cowboy_req, resp_sent} potentially leaking in loop handlers
Make examples use the new routing
add patch support to cowboy_rest
Fix chunked streaming of request body and improve speed
Merge branch 'rest_patch' of https://github.com/treetopllc/cowboy
Makefile verbosity tweaks