Merge pull request #728 from chrox/master

update k2pdfopt to version 1.64a
free cache that does not contain requested page area
Merge pull request #737 from houqp/master

cache bug fix
KUAL extensions added (since kindlepdfviewer will soon support all devices)
remove unrequired scripts
update to direct referencing of scripts.
SIDE-EFFECTS: this means /mnt/us/kindlepdfviewer/kpdf.sh is now the REQUIRED location as opposed to preferred.
Merge pull request #746 from twobob/master

KUAL extensions
add extensions directory in customupdate