Tweaks and improvements:

* In Edit mode, pressing right mouse button will now work as pressing Space key.
* In Edit mode, dragging with left mouse button in horizontal direction will work as pressing Right / Left keys (changing natural borders  suggestion).
* In Edit mode, two new ways of issuing 'Merge with previous' command have been introduced: 1) dragging up with left mouse button  and 2) pressing Z key.
* In Edit mode, clicking a word a second time will separate a pair provided the other border is naturally set.
* Included several puctuation marks for better "natural divider" guessing.
* Escape now closes Settings window.

Bugs fixed:
* In Edit mode, mouse highlight of the rightmost word would not restored if mouse left the control and came back to this word.
* In Edit mode, manually setting one border, then going to another pair and setting the opposite border would separate that pair.
* In Reading mode, pressing space would lead to separating a pair.