Add a ALfilterState method to process multiple samples at once
Use _mm_setr_ps instead of _mm_set_ps

Apparently _mm_set_ps loads in reverse order compared to _mm_load_ps, so
_mm_setr_ps should give what we really want.
Pass some DirectParams as function parameters
Use different parameters for HRTF mixers
Don't pass the DirectParams to the dry-path mixer
Don't pass the SendParams to the wet-path mixer
Move an HRTF mixer parameter and shorten a couple variable names