Added support for Excon
Add net net-http-persistent adapter

Using the url of the request to generate the thread pool key.
Specific dependencies for rubyntlm and puma

rubyntlm > 0.1.1, is causing Bad Response.
puma > 2.0.1, is not returning HTTP headers on HEAD requests.
Merge remote-tracking branch 'dim/master'
Excon adapter, fix to support 1.8.7
Merge remote-tracking branch 'frontfoot/master'

Conflicts:
	Gemfile
	spec/httpi/httpi_spec.rb
fixed timeout and proxy for em-http. closes #88.
raise an error for net/http digest auth. fixes #90.
Merge branch 'Full-NTLM-Support' of github.com:pmorton/httpi into pmorton-Full-NTLM-Support

Conflicts:
	httpi.gemspec
updated rubyntlm dependency
removed commented out specs