btText: äldre versioner att ladda ner

- Added: Text snippets can now optionally be formatted using simple Markdown. When inserted, they are output not only as plain text but also as HTML and RTF, so that the formatting is preserved if supported by the target program. This allows for simple formatting (bold, italics, etc.), links, and citations.
- Changed: Updated to Python 3.15.
- Changed: Dependencies updated.
- Changed: UPX is no longer used to compress the program files in order to achieve faster performance.
- Fixed: Privacy settings for Windows clipboard history and cloud synchronization are now respected even when copying or pasting fails.
- Fixed: Percent signs in database paths no longer cause unexpected issues.
- Fixed: With hotstrings enabled, accents such as ´ were inserted twice instead of combining with the following letter (e.g. to produce é).
- Fixed: A timing issue when pasting snippets could cause newly copied clipboard contents from other applications to be lost and replaced with older contents.
- Fixed: The installer can no longer accidentally update portable versions of btText, which could lead to data loss.

- Improved: The installer now ensures that btText is not installed into an existing folder that does not contain btText itself. New installations and updates are still possible without any problems.
- Fixed: Hotstrings now work more reliably during various system events, when switching between windows, and in conjunction with modifier keys (Ctrl, Alt, Shift).
- Fixed: Pasting into other applications now reliably checks whether the window still exists.
- Fixed: Changing the global keyboard shortcut might have caused a misleading error message to appear.