PHPLIB-288 Document how to specify singleBatch option with Find

PHPLIB-268 Add option maxAwaitTimeMS on getMore commands

Before PHPC 1.2.0, these options could only be specified as query modifiers.

This also updates Travis CI to pull 1.3.0RC1 until a stable 1.3.0 is available.

This also switches to container-based build environments, which allow installing multiple versions of MongoDB via the apt addon.