Updated README for PR #1045

Added info on how to configure Berkshelf for downloading cookbooks
cached from Github by the Berkshelf-API server
Merge pull request #1070 from svanharmelen/added-doc-for-pr1045

Updated README for PR #1045
Fix failing git spec
Fix failing error spec (bad rebase?)
Merge pull request #1075 from berkshelf/sethvargo/failing_tests

Fix failing tests
Add feature for updating a git location
Fix git location caching
Merge pull request #1078 from berkshelf/sethvargo/git_is_hard

Fix git location caching
Make Berksfile#has_key? honor --except/--only
Freeze lockfile constants
Remove stale Berksfile test
Move reduce_lockfile! to lockfile.reduce!
Create Lockfile#to_lock (super useful for debugging)
Use a Hash and less Ruby magic for finding transitive dependencies
Add a message that we are now resolving cookbooks
Use new has_dependency? Berksfile API
Make Installer#install a private API
Update json feature to include new output message
Wow... This test was just wrong
Switch logic in dependency?

I must have been on some serious crack when I wrote that logic...