New function bindings for opening/deleting files and for moving through the HDUs of a file

I have implemented new bindings for the following functions: `fits_delete_file`, `fits_open_table`, `fits_open_image`, `fits_open_data`, `fits_file_name`, `fits_movabs_hdu`, `fits_movrel_hdu`, and `fits_get_num_hdus`.

I have updated the documentation accordingly.

Cheers,
  Maurizio.