Merge pull request #303 from chrox/master

free blitbuffer as soon as tile is kicked out from cache
Merge pull request #308 from chrox/master

fix getAutoBBox failed bug
Merge pull request #310 from chrox/master

use pixels from reflowed page when doing OCR in reflowing mode
Merge pull request #311 from chrox/master

reactivate FFI blitbuffer module
rescale font size when fallbacks to fallback fonts
and make FreeSerif font the default font instead of DroidSansFallback

This patch should fix #272.