Merge pull request #268 from chrox/master

update koreader-base to include new djvulibre repo address
update koreader-base
Merge pull request #270 from hwhw/master

update koreader-base
update koreader-base
refactoring koptcontext creation function
add DHINTCOUNT in defaults.lua
It controls how many number of pages will be hinted in background
after one page has been drawn. Default DHINTCOUNT is 2.