reverb: Add wet/dry and improve the bypass.

The bypass isn't perfect because the sqrt in the wetdry section does't get
bypassed (so there might be a modest amount of gain when bypassed).

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
bitshrieker: Significant hand tuning with synthetic signals

Works well with qsynth but needs to be tested on a real guitar signal.
Possibly we will needs a bass boost...

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
gtk_knob: Improve wheel mouse handling

With some hardware event->direction always comes back as GDK_SMOOTH_SCROLL.
For now we cheat if this happens and use the sign of the vertical delta
instead.

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
gitignore: Trivial update

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>