LineContents: add line2fbf

[PhosCity]

fixes #5

This PR adds a new method to split lines to frames. Supports for move, transforms and fade. Returns a list of lines.

Additionally adds a method to lerp fade value and return alpha and lerp colors in RGB colorspace(it would only lerp using HSV earlier). Also fixes lerp for rectangular clips.

You could do something like this to convert line2fbf in your script.

main = (sub, sel) ->
  lines = LineCollection sub, sel
  toDelete = {}
  lines\runCallback ((lines, line, i) ->
    data = ASS\parse line
    fbf = data\line2fbf!
    lines\addLine split for split in *[line for line in *fbf]
    toDelete[#toDelete+1] = line
  ), true
  lines\insertLines!
  lines\deleteLines toDelete

The code above only converts the line to fbf but if you desire, you could also loop through each line the method returns and do your own stuff before inserting the line to subtitle.