clock.lua module added

[trentgill]

Fixes #339

This is a basic implementation of the the norns clock module. It's based on the initial implementation by @artfwo rather than the recently updated one. I will lilkely revisit this before 3.0 to refine some things. Especially using the CV input as the clock source needs some refinement (it seems quite drifty, and perhaps there are double-triggers).

Usage is similar to norns, but with some key differences & helper functions that are specific to the crow workflow:

--- All of the basics are identical to norns:
myclock = clock.run(function()
  while true do
    print'hi!'
    clock.sync(1/4) -- synchronise to the next 1/4 of a beat
  end
end)
clock.sleep(n) -- sleep for n seconds
clock.suspend() -- suspend until manual restart
clock.resume(myclock) -- resume a suspended coroutine
clock.get_beats() -- beats elapsed since starting
clock.get_beat_sec() -- convert beats to seconds at current tempo

--- Differences on crow are mostly about syntax relating to tempo & clock source
-- internal timebase (default)
clock.start() -- selects the internal timebase & starts the clock (this is effectively run at init())
clock.stop() -- selects the internal timebase & stops the clock [This doesn't actually stop though?]

-- tempo just works as a variable
clock.tempo = 160 -- set internal tempo to 160bpm (ignored if using external source)
print( clock.tempo ) -- print the current tempo (uses external source if active)

--- CV inputs as timebase
-- when choosing clock mode, internal timebase is disabled
input[1].mode('clock',1/4) -- set timebase to use input jack 1, where each trigger == clock.sync(1/4)

--- output helpers: create a tempo clock with one line
output[1]:clock(1/4) -- set output 1 to pulse every clock.sync(1/4), ie 4 times per beat
-- by default output.clock sets the ASL action to pulse(), but you can reassign it
output[1].action = ar() -- now the clock will trigger an envelope instead of a pulse

[tehn]

this is super great! only issue:

clock.suspend() -- suspend until manual restart
clock.resume(myclock) -- resume a suspended coroutine

both of these will be deprecated. @artfwo and @ngwese agreed (in vid meeting recently) that they were not quite what was required for a particular use case--- and then there weren't really any sensible remaining use cases for these.