Marginalia Annotation

_From @cubap on October 16, 2015 5:32_

Several types of interest areas may be important to capture, but may not be part of a cohesive enough to be part of a `layer` as in #1.
1. Dry glosses and other comments or decoration between or near lines that relates to a specific part of the text. This may have a selector on the canvas for its content and target, as well as both transcribed content and commentary as to its impact or purpose.
2. Written comments in margins that edit the main text in some way and may point specifically to text, canvas regions, or even out to other locations in the manuscript.
3. Doodles and other graphical features that will be described, but not transcribed.
4. Codicological features like catchwords may be noted and tied to other canvases.

_Copied from original issue: cubap/TPEN3#2_