Several Makefile cleanups.

Added PKG_BUILD_PARALLEL for faster compilation.

Several size optimizations applied.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Signed-off-by: Ted Hess <thess@kitschensync.net>

fix Makefile chmod (644)
replace MD5SUM with HASH
add PKG_MIRROR_HASH when PKG_SOURCE_PROTO:=git

(PKG_SOURCE_PROTO:=svn tarballs are not reproducible for now)

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

Signed-off-by: Nicolas Thill <nico@openwrt.org>