protocol hierarchies
common.hpp should be only included from top-level headers
a bit more conscious names
explain why plugin cannot be loaded
fix void slot service behavior
do not allow writing to dead client channels
issue #24
zeromq 3.x doesn't ship C++ bindings anymore as part of main pkg

Change-Id: I8220315c369efee7201ceb4d8506f6eaac81322d
Merge pull request #25 from redbaron/master

fix build with recent zeromq
no need to fetch zmq.hpp for travis-ci builds anymore, thanks to @redbaron
some sleek styling
fix issue #26 - convert mpl's long size to size_t before comparison
resolve issue #23: do not try to create any paths, just complain about their absence; recreate the runtime path in initscript; store engine endpoints in the runtime directory itself
more result types and descriptions for the common service messages
minor cleanup, naming, styling
app_t implementation doesn't use any public messaging, drop the dependency
Merge branch 'master' of github.com:cocaine/cocaine-core
resolve coverity defect #14137: unhandled bad_format_string exception
might be a  workaround for coverity defects #14110-14114: resource leak in operator[] access to boost::unordered_map
Merge branch 'master' of github.com:cocaine/cocaine-core