Force build configuration choice; update docs

It was getting to easy to choose the buildroot default. This commit also
adds info about caching downloads which is really important.
rpi: Enable hardware interfaces (gpio, i2c, spi)
erlinit: bump version to v0.2.0
rpi: add erlinit.config to force controlling tty

This is needed to select between seeing the prompt on HDMI vs. seeing
the prompt over the UART.
nerves-env: add erl_interface to the library list
syslinux patch just got accepted into buildroot
Initial i3 commit
generix-x86: Add lots of patches to get x11 to work
Turn off tar.gz, etc options that are not needed anymore for i3
Enable evdev to get keyboard and mouse working
Delete patches that have been merged into upstream br
No longer need this patch
Use buildroot to patch buildroot

This makes the patching process more robust. Errors weren't being
caught before.