System Independent

PageTranslate-2.1

* DuckDuckGo backend added.
* Google Cloud Translate available, but untested.
* Annotations enabled for text selection mode.
* Target language is now set for translated paragraphs.
* Internal rewrites.
* FauxRequests fallback might now work for all backends.
* Translate-python has been removed (Msft now via D-T).
* Undo unicode glyphs in dropdown (hiccup in AOO).
* DeepL and SysTran fixes.
* Added some automated tests for services.

PageTranslate-2.0

* Add SYSTRAN backend.
* Introduce ArgosTranslate binding.
* Added LibreTranslate via D-T and internal.
* Select-only mode (disable whole-doc traversal).
* Added pt-BR as default language in menu.
* Introduce annotate/comment mode to preserve untranslated text sections.
* Refined backend code, and lots of pylint fixes.
* Enabled setup buttons in options dialog.
* Separate standalone version: tk_translate.
* Fix DeepL web scraper.