v.5.8.1

[eao197]

A new type of message sink added (#67).

A couple of new methods for so_5::agent_t for accessing agent- and coop-related disp_binders (#14, #71).

More detailed descriptions of new features can be found on the corresponding Wiki page.

Fixes for #68, #69, #70.

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This discussion was created from the release v.5.8.1.