Added :bitbucket as a new :git source
Using HTTPS instead of SSH
Merge pull request #2897 from mcorp/bitbucket

Added :bitbucket as a new :git source
Refactor Bundler::Dsl#add_*_sources

Refactored `#add_github_sources` and `#add_bitbucket_source` into
`#add_git_sources`.
Hardcode the list of options for `bundle install --trust-policy`

The reasoning behind this is that OpenSSL gets loaded up in a situation
where we just want to show the help banner for the install command.

Seen as the security policies on the rubygems repo haven't been changed
in over two years, it's safe to just hardcode the values, thus generally
speeding up Bundler commands, most notably in JRuby.

Closes #2950
Add AlmostNoSecurity to trust-policy and fix doc links to Rubygems.