Use gtk_text_buffer_begin_user_action() and end_user_action() to group
all text buffer operations triggered by a single editing operation.
Connect to the buffer's "end-user-action" signal instead of to
"changed", "apply-tag" and "remove-tag" separately, so we only update
the text proxy once per user editing.
instead of using the toggles only to change the style of selected text.
Introduces a list of "insert tags" in GimpTextBuffer that is applied
on newly inserted text if it exists. Clear the list on each content
or cursor/selection change, so we always display wthe style at the
cursor unless the buttons were clicked explicitely.
- keep around tags for styles in GimpTextBuffer. For now only bold,
italic, underline and strikethrough.
- add GimpTextStyleEditor, a widget which allows setting tags on
a GimpTextBuffer's selection.
- add serialize/deserialize code to/from pango markup using
GtkTextBuffer's rich text (de)serialization infrastructure.
Doesn't produce or handle <span> yet.
