add mmexternal skeleton (support external message mod plugins)
mmexternal skeleton was not properly build
add skeleton for python message modification module
make mmexternal read synchronously from external program
introduce new API for modifying message object (just a skeleton)
mmexternal: funnel program reply through to msg object
Merge branch 'master' into master-mmexternal
milestone/mmexternal: msg understands JSON response at top level
Merge branch 'master' into master-mmexternal
milestone/mmexternal: change to use message passing interface

this is required as we need to modify the messages; this also means
tempates can not be used when sending data to it.
milestone/mmexternal: permit update to rawmsg property

this is the first PoC
cleanup (forgotten in previous commit)
milestone/mmexternal: support replacing msg property, fix stall in mmexternal
add capability to modify $! JSON part
mmexternal: add "interface.input" config parameter

permits to specify what should be passed to external program
mmexternal: remove remains of template use

No longer needed/possible due to message passing mode (leftover)
python mm skeleton: remove LF from interface call before processing message
fix memory leak in message modification
Check for "rst2man" and "rst2man.py" (Fixes #51)

docutils installs "rst2man.py" per default, so we need to check for both
variants:

 * "rst2man" when using python-docutils from Ubuntu

 * "rst2man.py" when using docutils from upstream
Merge pull request #54 from Whissi/issue_51

Check for "rst2man" and "rst2man.py"