smart Home key

[cben]

Don't select indentation, nor 1. or > on first press. (Same for Shift+Home.)

[Inspired by IDLE and this review of Texts.io:

Number/bullet management. Hit Tab or Shift-Tab anywhere in numbered/bulleted paragraphs to indent or de-indent them. If you hit CTRL+SHIFT+HOME, and emphasize a text, Texts is intelligent enough to not select the automatic numbering itself either; these are small details, but they really do improve the writing experience.

though that I think talks about applying 1. *emph* instead of *1. emph* when you did have the 1. selected?]

[Marking "upstream" because these ideas belong in CodeMirror and/or SimpleMDE]