Initial support for single-line regular expressions matching
Fix crash when closing a document with visible infobars

Apparently the ::unrealize symbol is sent too late, after we destroyed
the widget and freed the GeanyDocument, and some signals like
::focus-in-event can still be fired on the widget after that.

So, properly use the ::destroy signal that is supposed to be fired when
others should release references to that instance.
Adding message to client/log keywords to SQL type
Add support for single-line regular expressions
Add UI elements to control single-line regex settings
Update the documentation for single-line regular expressions
Merge branch 'single-line-regex'