turn off colors if NO_COLOR is "true" or TERM is not "xterm*" or STDERR
is not connected to a terminal, but ignore TERM and STDERR if NO_COLOR
is set to "false" explicitly.
Fixes#69
turns out that the README.md explains that "... licensed under MIT ...
the LICENSE does not have to be bundled as long as ..." but the scripts
themselfs don't mention any license.
fixed that by adding a one line mention of the used license and the two
lines explaining that the header comments have to stay intact.
