[Investigation] Supporting multiple ATEM SDK versions

[SteffeyDev]

It would be great if we could support older versions (#151) so that you can use the latest features of AtemOSC while using an older SDK version. However, there are two major obstacles:

1. The ATEM SDK files are compiled into the binary and built against, and thus we would have to produce multiple output versions, 1 for each SDK version we support AFAIK.
2. Newer versions of the ATEM SDK may have breaking changes that require our source code to change for it to compile. We would need to figure out how to support multiple code paths while still allowing it to compile. May require compile-time or pre-compile transformations.