Added boxes-pkg.openwrt by Lu Weifeng to build and package boxes on OpenWrt
Allow user to add flags to CFLAGS and LDFLAGS

To build on Mac OS X: `make CFLAGS_ADDTL=-m32 LDFLAGS_ADDTL=-m32`
Updated commit to address CFLAGS issue: https://github.com/ascii-boxes/boxes/pull/10#issuecomment-59661052