Fix #60; various other fixes; start work on custom documentation (#47).

Add a more helpfull error message when the pdf location is write prot…

…ected; fix #51

Allow caching and correct hashing of (animated) GIFs; don't compress …

…GIFs anymore (fix #52, #54).

(Attempt) to fix new error that arose with 1.17.3/1.17.4.

Fix unicode encode error on windows (#50).

Fix unicode encode error on windows (#50).

Remove debug-prints that I forgot to remove.

Ensure image file names make sense and are shorter than 160 characters; 

fix #48.

Add support for unicode emoji shortcodes as well as custom emojis; fix …

…#42.

Add option to the python API to check whether the HTML is valid, if t…

…idylib is installed; partially fix #40.