Bulk write API

RUBY-676
Handle Bulk API versus server version / max_wire_version
RUBY-667 user command helpers and update to auth tests
Add support and error for digestPassword option
minor: hash args style updates
minor: no need to rescue error in auth test
Document new user command private methods as such
Merge branch '1.x-stable-ruby-676' of github.com:gjmurakami-10gen/mongo-ruby-driver into gjmurakami-10gen-1.x-stable-ruby-676
Fix remove_all_users command to match current server code
minor: fixing license date per request from legal
minor: fixing auth tests for logout failures
minor: fixing missed instance of renamed variable
README updates to fix grammar, add notes on support, bugs, security issues
minor: removing useless ternary operator in read pref module
RUBY-614 support for SASL PLAIN authentication (LDAP)
RUBY-614 test coverage for SASL PLAIN support