Let 'o' expand/collapse folded text.
Let tags intrude into subject in thread display.
Put standard tags into a common structure.
Revert "Remove hack that stops drawing one column early."

This reverts commit 1d4fd7078c586df59efcadc72a0b7178e9609015.
Draw the space preceding a tag in the same call as the tag.

This prevents drawing the space then finding out there is no room for
the tag, leading to a situation where the space would clobber the
subject text in the penultimate column, but the first character of the
tag would not clobber the final column.
text_entry: Move remaining state into info type.
text_entry: Support undo.