Allow using multiple constructor arguments for configuring elements

Disable undocumented ability to specify aliases as arguments
for constructors, e.g. parser:option("-f", "--foo"), and instead
order properties and pass constructor arguments to them.
E.g. parser:argument("foo", "A foo that bars") sets argument
name to foo and description to "A foo that bars".

TODO: remove "aliases" property, instead allow setting several
names in one string by separating them using space.
TODO: reorder properties so that most useful ones could be used
as constructor arguments.

spec/help_spec.lua

@@ -53,8 +53,7 @@ An epilog. ]], parser:get_help())
          :args "2"
       parser:argument "maybe-fourth"
          :args "?"
-      parser:argument "others"
-         :description "Optional. "
+      parser:argument("others", "Optional. ")
          :args "*"
 
       assert.equal([[