Made to call rebar.cmd in Windows

In Windows, rebar executable is rebar.cmd, which does not exist on Linux/Unix, not rebar.
Made to use rebar.cmd if it is there.
Merge pull request #65 from redpine50/make_cygwin

Made to call rebar.cmd in Windows
Cleanup handling of local shell functions

Also add some more documentation about the shell environment.
Update version history for v0.8
Make lists of positive integers an "atomic" type

This is an experiment to test whether we can have integer lists
strings as an "atomic" type. Should we have list of valid unicode
characters instead?
Make lists of positive integers an "atomic" type in the compiler

This is still an experiment to test whether we can have integer list
strings as an "atomic" type.