WIP: convert each islet to a gen_server
WIP
Exec islet with dropped privileges

Replace start-stop-daemon with a new executable, islet_exec. The code
calls setuid/setgid to drops privs then execs the islet.
start-stop-daemon requires the uid/gid be defined in /etc/passwd,
islet_exec does not.
Describe islet environment using nested records

Instead of using a proplist of proplists, return a nested record and
simplify the environment creation.
Describe islet environment using nested records

Instead of using a proplist of proplists, return a nested record and
simplify the environment creation.
Merge branch 'fix-atoll' into spawn

Conflicts:
	src/islet.erl
Truncate README and an example

Prepare for adding documentation.