get_message, new_from_message without memcpy

[plesskem]

Proposed extension of the fortran grib api:
2 methods which are already included in the C interface and used to directly access the coded message in main memory
these methods are for example practical for sending/receiving coded grib messages with MPI

• grib_get_message
  returns a fortran pointer to the coded message (character) of a grib_handle
• grib_new_from_message_no_copy
  creates a new grib_handle with a data buffer pointing to a provided coded message (character or integer)

[FussyDuck]

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