Added script which handles kernel upgrades.

This fixes #88 and #89.
Part of the code was taken from goranche's pull request.
Make sure that the 'kernel=' line is on a line by itself.
Updated README.md

just removed the “copy new kernel” instruction and replaced with a line
explaining stuff happens automatically
Make sure there's a /boot/kernel.img present on the image.
Also ensure the initramfs statement is on a line by itself.

Also added '-e' to the echo statement to make sure \n is interpreted as newline.
Inform the user the progress on the kernel actions.
Removed the '-e' parameter to echo since it caused '-e' to be put in config.txt.
Merge pull request #114 from diederikdehaas/handle-kernel-upgrade-v2

Added script which handles kernel upgrades.