Add support for passing integer(8) values to mpas_log_write.

[jim-p-w]

This PR allows callers of mpas_log_write to provide values of type integer(8).

The placeholder specification is $w for integer(8) values, as opposed to $i for integer values.

I ran a test where I interspersed integer and integer(8) values, e.g.

integer, dimension(:), allocatable :: intarray
integer(8), dimension(:), allocatable :: int8array
...
call mpas_log_write('SMIOLf_get_var error $i i81:$w int1:$i i82:$w int2:$i i83:$w', intArgs=[local_ierr, intarray(1), intarray(2)], int8Args=int8array, messageType=MPAS_LOG_ERR)

[mgduda]

@jim-p-w Can you add more detail to the commit message?

[jim-p-w]

@jim-p-w Can you add more detail to the commit message?

@mgduda How about:
Allow passing values of type integer(8)/integer(kind=I8KIND) to mpas_log_write.
The string $j is used to identify integer(kind=I8KIND) values.

I'm open to suggestions about what the commit message says.