[Documentation]: `API.md` out of date

### What happened?

## Description

`API.md` states:

```md
use h5mpi, only: hdf5_file, HSIZE_T, HID_T

type(hdf5_file) :: h
```

The module seems to have been renamed to: `h5fortran`, as seen in the example.

Can't tell if anything is out of date as well.

### Relevant log output

```shell

```