Move contributions information into CHANGELOG.md and get rid of CONTRIBUTIONS.md. Also make sure the names of our awesome contributors are reflected in addition to their Github profile.
Merge pull request #1450 from opscode/sersut/changelog

Updates to CHANGELOG and CONTRIBUTIONS
set ENV vars for http proxies
percent encode @, : in proxy user/pass
test proxy env vars available for shell_out
rename configure_environment_variables to configure_proxy_environment_variables
update for setting proxy env vars