Bump base (#4988)
Bump base (#4988)

Mainly for the switch to the C BB by default on Kobo/Kindle/PB

But also includes:

CI tweaks: https://github.com/koreader/koreader-base/pull/907
           https://github.com/koreader/koreader-base/pull/911
DjVu tweaks: https://github.com/koreader/koreader-base/pull/909
SDL2 tweaks: https://github.com/koreader/koreader-base/pull/910
mwoz123/koreader,poire-z/koreader,poire-z/koreader,koreader/koreader,koreader/koreader,NiLuJe/koreader,Frenzie/koreader,NiLuJe/koreader,Hzj-jie/koreader,Frenzie/koreader,mihailim/koreader,Markismus/koreader,pazos/koreader