@geek11: two word about KoboTouchExtended vs kepubify:
1. speed is not an issue for me. Yes, as an user sometimes I feel Calibre slow. Python *is* slow, but it's more simple to code and to maintain. A saw a lot of motivated programmers that refuses to code something that is not near to the metal, and they will soon abandon the project because it's too complicated to code, and no one will continue to maintain it for the same reason. Especially if it's written in that crap language that is C
2. a Calibre plugin is much more powerful, since it integrates not only with a mere converter, but with a full suite, thought to catalogue, add metadata and send books properly to the devices.
3. you can't know what will happen if you transform the HTML, even if you simply fix the syntax and remove useless tags. HTML renderers are various and unpredictable.For example, if you remove an apparently useless tag, you could break some css rule. The keyword is: option. You can add it as an option, maybe true by default, but not force it.
4. don't take it personally, but I know dadivfor by a lot of time. He is skilled in epub and kepub format, Calibre, Kobo and many other e-ink related stuff. You... well, I read a few posts, but you seems to me very noob. The fact that you don't use Calibre plugin but a self-made solution, not configurable, and thinks that Calibre is a crap because is slow confirms my opinion. If you want a fast Calibre plugin, you can use Cython. Very simple and powerful. You don't need C++.
I want to be clear, I have nothing against C++. It's a fantastic language, very powerful. But it's complicated, difficult to maintain, difficult to get help by someone else and it's prone to errors, memory leaks and security flaws if bad programmed. Python on the contrary is a pleasure to code, is readable, it's more simple to maintain and to avoid errors, and you can speed it up with Cython. Or with Python C API, if you want to be more near to the metal.