STL Containers: version 2

This release adds support for STL Containers in a second style which does not break preexisting code but satisfies user expectations for both setting and receiving STL Containers from Lua using Sol. It is a breaking change from how it was handled previously by default, and the old behavior can be requested using the new as_table marker on a container type when pushing data to Sol or retrieving data from Sol.

Everyone is encouraged to upgrade to the latest immediately, and thanks to everyone who reported bugs with the previous haphazard implementation!