Do not remove duplicated Set-Cookie entries

This commit closes #195, closes #199, closes #246.
Mimetype lookup expects lowercase extensions

We handle extensions in a case-insensitive manner when looking
for a mimetype for a file. Extensions are thus lowered.
musnt is not the correct contraction of mustn't - use must_not instead
Return "400 Bad Request" instead of crashing process on incorrect queries like /%qq
Convert headers to lowercase
Merge pull request #315 from tokenrove/correct-header-case

Convert headers to lowercase
Add a few more infos to the .app.src for private use
Fix the markdown for the README
REST: Fix the status code sent if the content type isn't known
Merge pull request #297 from puzza007/master

Correct spelling in rest callback name
Fix a small typo in the rest_init error message
Merge branch 'master' of git://github.com/josevalim/cowboy
Fix dispatch documentation with regards to the <<"*">> path
Merge branch '400_Bad_Request' of git://github.com/blinkov/cowboy
Check for errors when calling Transport:send in the websocket protocol

In some situations, the underlying socket might become "half-open" in
which case the websocket will stay in a waiting state indefinitely. The
detection of this state requires checking for errors when calling send.
Do not try to keep-alive when using HTTP/1.0
Cosmetic changes to various documentation files
Merge branch 'fix/websocket-check-error-on-send' of git://github.com/tillitech/cowboy
Fixed onrequest path-related issue
Merge branch 'onrequest' of git://github.com/saleyn/cowboy