Add Group 4 (CCITTFAX4) compression to TIFF output

[woolite64]

This PR addresses #1207, with one concern mentioned below. Any insight/feedback is appreciated.

It isn't clear to me why the test case required .toColourspace('b-w') to compress properly. If we check the input document's metadata, the space is already 'b-w'.

Output of fixtures.inputTiff metadata:

{
  format: 'tiff',
  width: 2464,
  height: 3248,
  space: 'b-w',
  channels: 1,
  depth: 'uchar',
  density: 300,
  hasProfile: false,
  hasAlpha: false,
  orientation: 1
}

[coveralls]

Coverage remained the same at 99.007% when pulling b8e2aca on woolite64:master into 6d2da2b on lovell:master.

[lovell]

Hello again, thanks for this, looks great. The default colour behaviour is to convert to sRGB, hence the need to use toColourspace('b-w'). Perhaps this could/should be inferred from the TIFF output options?