Split dat1Type into two routines

So that you can convert the output of dau1CheckType back into an
HDS enum.
Improve datPut error messages
Routine to deal with type information

Currently just calculates bad values.
Do _CHAR to numeric type conversion

HDF5 does not do this but HDS supports it. We manually
convert from _CHAR type to the underlying number format.

PAR library relies on this behaviour.
Use hdsbool_t type for Logicals
Use hdsbool_t explicitly for _LOGICAL

Rather than straight int.
More notes in readme
Need the Fortran interface header files