DDS — DDS ISSUE# 52] Provide for zero copy access to data

Ref-121 Add_a_return_loan_operation_to_datareader

For high-performance it is desirable to use a zero-copy API on the
receive side where the middleware can "loan" buffers to the
application on the "read" or "take" operations.

However the use of "zero-copy" requires a mechanism for the
application to indicate that it no longer needs access to the "loaned
buffers"

One possibility would be to an operation DataReader::finish or
DataReader::return_loan that takes the SampleData and SampleInfo
sequences as parameter and indicates to the middleware that the
application is no longer accessing the buffers in the corresponding
sequences.

Another possibility would be to add a separate API for read/take

**PROPOSAL**

No concrete proposal yet

see below