Update library reference to support Pi 4

Updated matrix library to use newer commit with additional features

The existing commit reference for hzeller's library points to a version of which doesn't support the recently released Raspberry Pi 4. Edited the script to point to the new commit before running it and it started working fine on the Pi4.

Fixes PiTFT Installer for Buster

Added Buster to Raspbian experimental list

libgpiod.sh doesn't assume Python 3.5 anymore

aplay: change rate to 44100 to avoid unnecessary CPU usage

fix for https://github.com/adafruit/Raspberry-Pi-Installer-Scripts/issues/49#issuecomment-491151983

Add -f S16 option

Update libgpiod.sh

small patch to keep apt-get from failing on board-specific imports

pitft: add ExecStartPre sleep of 10 seconds before starting fbcp

cd "$target_homedir" instead of hardcoded username (fixes #35)

add some hacky file copies for libgpiod python bindings

add @ladyada's libgpiod install instrux to script

add optional aplay-at-startup service to i2samp.sh

Installs service file in /etc/systemd/system/, then disables.  Prompts
user to enable, and triggers reboot dialog if installed.

Import occi util from Adafruit-Occidentalis repo

rgb-matrix.sh: use newer sha1 of github.com/hzeller/rpi-rgb-led-matrix

Keep cron & install ntp

add service unit for managing fbcp under systemd

Checks if we're under systemd, and if so, ensures that fbcp isn't
mentioned in /etc/rc.local, and installs a new unit file to start
fbcp at boot, after network.target.

If not under systemd, retains the old rc.local behavior.

I note this is the only place that the $SYSTEMD var actually seems to get
checked.  I can't, at this time, vouch for what would happen on a sysvinit
box.

Add execute permissions to all scripts

Backups excluded.

just breaks things. sorry to the 1% who have nonstandard apt repo needs

Keep cron & install ntp, so time tasks are still possible

Set C99 for Raspbian jessie