Improve colors of status messages.

Do not assume that the background is dark and do
not use white.
Add readUTF8() and writeUTF8() handlers.
Add support for redirection.

Allow sh() to accept, among the options, a record
with a "redirect" field, which can be used for
output redirection.
Add to sh() all the features of "do shell script".

Add support for running a shell script with
administrator privileges.
Add support for redirecting the output.
Add a flag for altering line endings.