Add a tweak to change the image compression quality used by the content server when it makes thumbnails.
Use much less memory when reading and writing cache
More cache work -- remove some code, get rid of old file.
Make metadata cache reading slightly more robust
Merge branch 'master' of https://github.com/cbhaley/calibre

Add a tweak to control quality of thumbnails generated by the content
server.

Also improve cache usage performance of the wireless device driver.