Set default 'cre_storage_size_factor' to 20 (#3732)
Set default 'cre_storage_size_factor' to 20 (#3732)

Increase default crengine in-memory cache sizes to avoid pack/unpack
of chunks that is known to be the cause of bugs (rendering, cache
re-use...).
Hzj-jie/koreader,koreader/koreader,NiLuJe/koreader,koreader/koreader,pazos/koreader,poire-z/koreader,Frenzie/koreader,Frenzie/koreader,houqp/koreader,mwoz123/koreader,Markismus/koreader,lgeek/koreader,mihailim/koreader,poire-z/koreader,NiLuJe/koreader