basic_filters: optimize RC highpass & bandpass filters
For both RC12 and RC24 filter types: handle lowpass separately, because we can then calculate highpass & bandpass with less operations.
This shouldn't affect the performance of lowpass, but probably will make highpass and bandpass a bit faster.
basic_filters: further optimization
Use qBound in formant, and return early from calcFilterCoeffs so we don't do needless calculations
basic_filters - even more optimization
Use more efficient interpolation, optimize some calculations
basic_filters: replace div with mul
What's this strings for Monstro
Merge pull request #897 from diizy/whatsthis

What's this strings for Monstro
FxMixer: rewrite mixer routing
Fix qstring arg
Receive arrow
Update channel send model names properly
Merge pull request #902 from diizy/fxmixer

FxMixer: rewrite mixer routing
Merge pull request #895 from diizy/filters

basic_filters: optimize RC highpass & bandpass filters
DspEffectLibrary: fix stereoenhancer
Use channel -1 for GUI-generated MIDI events, fixes #807
Merge pull request #909 from diizy/stable-1.1

Some fixes: StereoEnhancer, Midievents
Lmms_math: add dBV conversion functions (for future use)
Monstro: improve accuracy of env release
Merge pull request #910 from diizy/stable-1.1

Math, Monstro
Trailing spaces