BUG-472: Import OpenEXI nagasena-0000.0002.0035.0

This imports the OpenEXI nagasena library, on top of which the
implementation will be built.

Change-Id: I4ec0fc637f390fe14451c439870ec1846934ebbb
Signed-off-by: Robert Varga <rovarga@cisco.com>
BUG-472: Add EXI codecs without wiring them

This patch implements the EXI codecs to be used in the NETCONF pipeline.
No wiring into the protocol stack is done in this patch.

Change-Id: Ic708ef26d92e138f8269a49a2759f01d88085bf1
Signed-off-by: Robert Varga <rovarga@cisco.com>