Add cow_http_te module for streaming chunked and identity TE

Imported from Cowboy and then optimized with a more
efficient interface amongst other things.
Improve specs in cow_http
Add cow_http:request/4 and cow_http:version/1
Remove a warning when running all.sh
Update cowlib to 0.6.0

Adds chunked transfer-encoding support plus a few functions imported
from Cowboy. Also adds a function to build requests for clients.