Use vararg to pass arguments to command

[y5nw]

There are some other minor changes:

• Multiple spaces have the same effect as a single space (i.e. echo foo bar - with multiple spaces - is treated as echo foo bar)
• The number of arguments is also passed to the command
• Command lookup has been changed to a table indexing operation.
• The echo command is added for testing, but I don't mind removing it if it is not desired.