Update to 3.0:
- cleaned up clock format editor;
- replace placeholders menu by dialog exposing some additional options;
- new placeholders, no longer based on strftime() syntax;
- added possibility to to use simple conditional statements and display results of script expressions;
- allow to override mode of possessive form of month name (using + or - infix);
- allow to show time from multiple timezones (displayed in tool tip by default);
- allow to display events (displayed in tool tip by default);
- allow to display only characters range of substitution;
- allow to access placeholder dialog from format fields;
- allow to toggle use of standard background;
- allow to embed clickable links;
- improved formats storage;
- some code cleanups and fixes.