- Changed option parsing so that `--alias` requires an argument and will
  fail with an error unless provided. Applied the same logic to
  `--separator`.

- Changed `finish` parsing to capture it as a variable flag during
  argument parsing.

  This could be extended so that if `finish` is already true, a second
  `finish` results in the word being added to the argument list.

  ```console
  $ git feature -- finish remote
  $ git feature finish finish remote
  ```

  This has not been done because it is a bit of an inconsistent handling
  for documentation purposes.

- Add handling of `--` to permit options or `finish` to be made part of
  the feature branch name.

- Since `finish` is now a variable flag, simplify the name-building
  logic to always use `concatargs "${argv[@]}"`. This means that
  `git feature finish ...` and `git feature ...` behave the same in
  terms of feature branch name building.

- Basically rewrote the man page to include better descriptions of the
  options as well as adding a GIT CONFIG section and additional EXAMPLES
  for the new features/behaviour.