Various updates
This MR contains several fixes/improvements:
- warning fixes for clang (hopefully without breaking MSVC again!)
- switching back to the system sin/cos functions for twiddles (less code and no real loss of precision)
- compact storage of twiddles in
sincos_2pibyn(only O(sqrt(N)) instead of O(N)). - use
sincos_2pibynfor twiddle calculation in some DCTs/DSTs, where sin/cos were called directly so far - size reduction in Bluestein plans by making use of symmetries.
@g-peterbell any comments?