Support building the plugin through CI

[synap5e]

It would be nice to support building the plugin through CI.

This would enable bugfixes/enhancements made e.g. through the github editor e.g. #32 to be landed much easier, help in cases where people are keen to contribute or tweak things but don't know how to build e.g. #25

It would also make tweaks like #22 trivial

https://github.com/obsproject/obs-plugintemplate appears to have OBS plugin building, so could be used as a base.

[synap5e]

Or just pull from the fork https://github.com/norihiro/obs-screenshot-plugin lol

[wkpark]

Please see #37
(based on the obs-plugintemplate work.)