* feat: allow adjustment of compiler threads

Compiler threads may be changed in the `Advanced->Compiler Threads`
menu. Defaults to the available cores - 1, but may be adjusted from 1 to
maximum cores. Compiler threads also have been changed to `background`
priority to prevent lock ups on start.

* fix: fix ctd when terminating compiler threads

Switch to BS:thread_pool to abstract thread management and avoid
overhead of killing and starting threads. Instead, only add jobs to
pool when the number of active and queued threads is less than the
limit. The reason it's total and not just active is to avoid the case
where all tasks are dumped into the thread pool since the thread pool is
at the hardware maximum.

During compilation, one manager job is spawned to handle task
allocation and the remaining threads do the compilation work.

This reverts commit 07d50a4.

revert: "feat: allow adjustment of compiler threads (#99)"

* feat: allow adjustment of compiler threads

Compiler threads may be changed in the `Advanced->Compiler Threads`
menu. Defaults to the available cores - 1, but may be adjusted from 1 to
maximum cores. Compiler threads also have been changed to `background`
priority to prevent lock ups on start.

* fix: fix ctd when terminating compiler threads

Switch to BS:thread_pool to abstract thread management and avoid
overhead of killing and starting threads. Instead, only add jobs to
pool when the number of active and queued threads is less than the
limit. The reason it's total and not just active is to avoid the case
where all tasks are dumped into the thread pool since the thread pool is
at the hardware maximum.

During compilation, one manager job is spawned to handle task
allocation and the remaining threads do the compilation work.

* feat: enable skipping startup shader compilation

Users can now skip shader compilation before it is finished. Shader
compilation will continue using backgroundCompilationThread setting.
Users are also warned that this can result in visual errors or
stuttering while shaders are compiling.

…ders into dev