introduced run_count var

[hq9000]

This PR introduces a run_count var that shows how many reruns (Alt+r) have happends after full stop (Alt+s). This var is available for user code which can use its value (distinguishing between run_count == 1 - first run and runt_count >1 - subsequent runs).

Example:

live_loop :control_loop do
  print run_count
  sleep 1
end

One application of this is to be able to "control effects dynamically", as discussed in this thread and is based on the idea of a workaround proposed here.

With run_count available, the problem of controlling FX is solved as follows

#experimenting with changing cutoff using a single command line
#by Robin Newman

set :st,sample_duration(:loop_amen) #store duration of the sample

with_fx :rlpf, cutoff: 120 do |c|
  
  # This is the original workaround:
  # set :cv,c #comment after first run from stop, before re-run
  
  # This is how how we do it with `run_count`, no need to comment the code!
  set :cv,c if run_count == 1
  
  control get(:cv),cutoff: 120,cutoff_slide: get(:st)
  #                        ^^^
  #               change this number and hit Alt+r
  #                you will hear the changes
  
  live_loop :loop do
    print run_count
    st=get(:st)
    sample :loop_amen
    sleep st
  end
end

[rbnpi]

Could be useful, although one potential problem. I'm not sure that the run count would be unique to a given code buffer. If you run a different code buffer to the one containing your example code and then switch that your example code buffer with the first one still running, then when you press run it will register >1 for the count.