Quote script args and with args with spaces

For #298

Arguments to script/script-file/script-url were not being quoted.

Additionally, arguments with spaces were not being quoted.

If arguments have spaces even if not containing expansion variables then
they are quoted.
Add documentation for arg quoting for #298

* describe quoting rules for parsing command string and script args.
* describe escaping for option values in commands and args
Merge pull request #382 from gschueler/feature/i298-script-args-fix

script args fix and argument quoting documentation

fixes #298