make it easier to edit around invisible text.
This also allows representing long lexemes with a single character to provide a
summarized view.

lines for change history and other markers mark individual lines.

SC_FOLDACTION_CONTRACT_EVERY_LEVEL.
Avoid processing lines multiple times.

Fix documentation to use correct ID attribute.

history. Tweak size of INDIC_POINT and INDIC_POINTCHARACTER. Let translucency of
INDIC_COMPOSITIONTHICK be adjusted.

in the margin or in the text.

it can differ between screen and print.
Add GetSelectionHidden to allow testing of HideSelection.