Yield the content length to the chunking block when able to

This is useful for progress checks when downloading files. Written so as to be
backwards compatible with the previous method.
Just yield, don't check arity you dolt
Reverse the order of chunking block args and make sure remaining data is accurate
change sanitized_url from string add to concat
minor proxy related optimization
Give an example of how to use these arguments in the streaming API
optimize query building
fix 'Proxy-Connection' header defaulting
convert port to string initially rather than repeatedly
Merge remote branch 'nate/feature/pass-content-length-to-chunking-block'
simplify building 'METHOD /path'
Release 0.6.0
Introduce support for HTTPS via a proxy.
move stub to Excon for versatility and add default/per connection mock setting
rework stubs to allow for block based responses
pull out basic tests and reuse to prove mocks turn off
tests cleanup

remove redundant helper requires
cleanup whitespace
Merge remote-tracking branch 'origin/master' into https_proxy
Document the usage of a proxy.
Respect the http_proxy ENV variable if it's present.