Shuffled around the capture loop to provide better facility
to add new 'fire next capture' options. Makes the looping
easier to understand.

As a consequence have re-added the keypress option which
has gone missing.

Have modified timelapse so a value of 0 tries to take images
as fast as possible (with slight delay to allow exposure to
work)
Merge pull request #99 from JamesH65/new_capture_loop

Shuffled around the capture loop to provide better updates and re-add the keyboard capture option
Added a signal mode to allow initiation of captures from another process.
Waits on SIGUSR1 between captures.

Fixed a possible issue with black frames in timelapse mode where
-tl 0 is used. Ensures the first frame has plenty of time to get its exposure
right.
Merge pull request #103 from JamesH65/signal_mode2

Added a signal mode to allow initiation of captures from another process...