Add support for red and blue pens

[myersjustinc]

v2.11 added support for two more pen colors (red and blue): https://support.remarkable.com/hc/en-us/articles/4413620362897-Software-release-2-11#article-heading-1

(The fork @naturale0 mentions in #12 (comment) includes support for these.)

As-is, I get the following error when I try to use 89b5cc3 on a document where I've drawn in red or blue:

$ python -m rmrl 'Quick reference.zip' 'Quick reference.pdf'
Traceback (most recent call last):
  File "/Users/jmyers/.pyenv/versions/3.9.6/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Users/jmyers/.pyenv/versions/3.9.6/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/jmyers/wtf/rm-todos/rmrl/src/rmrl/rmrl/__main__.py", line 53, in <module>
    sys.exit(main())
  File "/Users/jmyers/wtf/rm-todos/rmrl/src/rmrl/rmrl/__main__.py", line 44, in main
    stream = render(source,
  File "/Users/jmyers/wtf/rm-todos/rmrl/src/rmrl/rmrl/render.py", line 95, in render
    page.render_to_painter(pdf_canvas, vector, template_alpha)
  File "/Users/jmyers/wtf/rm-todos/rmrl/src/rmrl/rmrl/document.py", line 148, in render_to_painter
    layer.render_to_painter(canvas, vector)
  File "/Users/jmyers/wtf/rm-todos/rmrl/src/rmrl/rmrl/document.py", line 245, in render_to_painter
    self.paint_strokes(painter, vector=vector)
  File "/Users/jmyers/wtf/rm-todos/rmrl/src/rmrl/rmrl/document.py", line 238, in paint_strokes
    color=self.colors[color])
IndexError: list index out of range

[lckarssen]

Have a look in my fork or the one from @naturale0 who started the work. For me this worked (you can set the colours to whatever you want).

Edit: Oops, I just see you already mention @naturale0...