[Feature] Multithreading

[squattingmonk]

Nasher is currently single-threaded. While it is still fast because of the underlying tools, multithreading would increase the speed at which large modules could be processed.

[WilliamDraco]

I had an initial exploration of this. I stuck with the unpack module since I knew it best. A few thoughts:

• gffConvert appears to be the most appropriate process to parallelise, being repeatedly called over many files.
• This requires gffConvert to be {.gcsafe.}. This traces through gffToJson/JsonToGff -> fatal -> error -> display* -> displayLine ->display Category*
  Both of those procs with * above reference the cli object, which is a global and therefore blocking {.gcsafe.}. I temporarily replaced fatal and info (which also has a similar proc path) with echo just to test.
• Spawning many gffConverts worked, and put the CPU to 100% and begins to convert at a high pace, however unfortunately something always snags. Most often I got was parseJson errors, I imagine related to the buffer being overwritten by another thread?

That's just my run of experimentation at the moment.