Fix documentation and otp.mk rules.
Use /bin/bash explicitly to run all scripts.

On some systems /bin/sh points to a minimal shell that can't run bash
scripts.

E.g. on Ubuntu /bin/sh is a link to /bin/dash that fails to run lfetool
in some cases:

$ lfetool repl

/usr/local/bin/lfetool: 1134: shift: can't shift that many

Switching to /bin/bash fixes the problem.
Merge pull request #40 from ska80/dev

Fix documentation and otp.mk rules.