Implements the ability to blind update add to a set.
Adds a test for a blind update append when the record doesn't exist yet
Adds blind set removal, and a test that it works
Adds a test that removing something that's not in a set just fails
quietly
Adds ability to blind append and prepend to a list
Updates the prepend to list test to make sure order is preserved when
multiple items are prepended
Adds a map __merge update mode, to merge in map with the existing values
on the server.
Tries to add a test that doesn't work because of a bug in the underlying
cql library.  So doing an update with a dict __merge with a None value
will not be possible for the time being.
reverts so we don't need to change the update_context method for map, we
just allow the dict column Quoter to have get() and keys() methods
Fixes issue because params got re-ordered
updates tests that had broken because of arguments being rearranged
Merge remote-tracking branch 'upstream/master'
renames the map "merge" operation to "update" to be consistent with
the python dict method
Merge branch 'master' of github.com:dcosson/cqlengine into pull-159
updating dict docs
making the container update class selection logic more readable
adding documentation around blind container updates
updating changelog