improved: added "--prefix" option to be able to debug script

And run on Linux, too.
`cygpath` is emulated with a function.
refactoring: explicitly use "-v" option for awk
improved: added --verbose option

Use "--verbose" option to show versions for "show" and "find" commands.
refactoring: indented AWK scripts
improved: now package name can contain spaces

This will be used later (for `outdated` command).
improved: added "--wget-options" option
improved: added "outdated" command

To show outdated packages
improved: added "upgrade" command

To upgrade outdated packages
refactoring: code moved out to 'unpack' function
refactoring: code moved out to 'do_postinstall' function
improved: added command 'localinstall'