BSON grow module

RUBY-676 New write operation method for insert, update, remove
unfinish! uses @str.size instead of unrestored @cursor
b_end! fix plus clarity
finish! fix and simplify finish_one!
minor: hash keys should be of a consistent type
Merge pull request #264 from gjmurakami-10gen/1.x-stable-bson-grow

BSON grow module included in ByteBuffer
RUBY-695 When secondary not ok for cmds, reroute to primary and warn
RUBY-695 out is required for map reduce and can be an object