next generation rpi-build

Based on Rake
build: make executable
install stdlib as well
build: move download dir
admin.rake: finish addlib
use 'open_uri' instead of the 'http' gem
add 'admin update'
add commandline arguments to logfile
show temporary logfile name
re-display error caught by the logfile
unpack(): add support tar.bz2, tar.xz, zip
add gitweb_tarball()
unpack: fix default symlink
add menuconfig and diffconfig targets
github_tarball: add ENV parameters
add cross_compile()
add {pre,post}_install script support and handle no MODULES
starting README support
use 'patch' instead of 'git apply'

git apply dosen't always work when used in a non git directory.
Use 'patch' by default.
update :usage