- Replace the `get_free_unit` subroutine with the built-in
`newutin` option of the `open` statement.
- Replace `locatex` with just `locate` + an index offset.
- Replace `inside` with `contour%contains`.
- Merge `vmaxmin` and `vmaxmini` into a single subroutine
with optional arguments.
- Remove unused `range2rect`, `bubble`.
1. Use the `contour` type for limiter and plasma boundary
(rlim, zlim, rbnd, zbnd)
2. Replace `inside` with `contour%contains`
3. Replace `range2rect` with a `contour` interface
4. Remove the limiter module which just re-exports the limiter
as a global; instead just pass the contour object around
