Install script

[l0b0]

Should add a Makefile with the following targets:

• install-<script>, where <script> is one of the export script names, to copy <script>.sh to $PREFIX.
• install: Copy scripts to $PREFIX.
• install-crontab-<script>, where <script> is one of the export script names, to create crontab entries for the individual scripts.
• install-crontab, to run all install-crontab-<script> targets.

[l0b0]

Partial fix in a1d1398.