Added in build plugin.

[adamharrison]

Officially submitting the build plugin. Should work with any script that outputs normal gcc-style errors.

I'm officially switching editors at work to lite-xl for C++, so over the next few weeks, I'll iron out annoyances, and we should be good to go after that, hopefully.

[adamharrison]

Just realised this is substantially similar to the console plugin, those this one has the concept of build targets, which is similar to my old IDE.

I'll evaluate at the end, and see if it's sufficiently different to warrant submitting it.