Rename 'edited' hook to more accurate 'reflow'

Also under consideration was 'layout', but that has other meanings
whereas reflow is more specific:
https://github.com/mathquill/mathquill/pull/317#issuecomment-45383191

Just did:

    sed -i '' s/edited/reflow/g $(git grep -l edited)

and rewrote the README entry.

Recommend --word-diff-regex='\w+|\S' to view diff.
Rename API method 'redraw' more specific 'reflow'

The 'edited' hook was originally named 'redraw', and I mistakenly
renamed it in #241 thinking they should mean the same thing, but undid
that in the parent commit.

Just did:

    sed -i '' s/redraw/reflow/g $(git grep -l redraw)

and rewrote the README entry.

Recommend --word-diff-regex='\w+|\S' to view diff.
Merge pull request #325 from mathquill/rename.edited-to-reflow

Rename 'edited' hook to more accurate 'reflow'