This closes quotes in error messages when parsing arguments.
Test: Added tests to make sure the error message when parsing arguments is
as expected, as well as added a test to check parsing options.
Closes#52
Following the Fuchsia CLI Tool Rubric
(https://fuchsia.dev/fuchsia-src/concepts/api/cli#option_delimiter),
this adds support for "--", which denotes the end of the options list.
All arguments that come after this point will be treated as positional,
even if they begin with "-".
Closes#58. Closes#59.
