Merge pull request #209 from dkogan/master

zsh completion: FILTER-ONLY fields excluded from -p strings
userspace/sysdig: always notify the formatter of the end of file
userspace/sysdig: flush cout to print the event

When the format is JSON, the last event received is not printed
until another event is processed or sysdig terminates.
userspace/libscap: handle trace file with no events
sunday afternoon project: little framework for modular protocol decoding
Merge pull request #211 from ret2libc/trace-without-events

userspace/libscap: handle trace file with no events
add two files that were missing from the previous commit
fix building of libscap on archs w/o live capture support (*BSD, Hurd)
fix build after d5b334cebb96840885f6a5cd7557dd4672bfd931

without this, the build will first fail with

In file included from /home/evgeni/Devel/sysdig/userspace/libsinsp/sinsp.h:84:0,
                 from /home/evgeni/Devel/sysdig/userspace/libsinsp/chisel.cpp:31:
/home/evgeni/Devel/sysdig/userspace/libsinsp/fdinfo.h:160:47: error: ‘sinsp_fdinfo_t<int>::callback_type’ has not been declared
  void register_event_callback(sinsp_fdinfo_t::callback_type etype, sinsp_protodecoder* dec);
                                               ^
userspace/libsinsp/CMakeFiles/sinsp.dir/build.make:54: recipe for target 'userspace/libsinsp/CMakeFiles/sinsp.dir/chisel.cpp.o' failed
make[2]: *** [userspace/libsinsp/CMakeFiles/sinsp.dir/chisel.cpp.o] Error 1

and later with

/home/evgeni/Devel/sysdig/userspace/libsinsp/fdinfo.cpp:196:6: error: specializing member ‘sinsp_fdinfo<int>::register_event_callback’ requires ‘template<>’ syntax
 void sinsp_fdinfo_t::register_event_callback(sinsp_fdinfo_t::callback_type etype, sinsp_protodecoder* dec)
      ^
userspace/libsinsp/CMakeFiles/sinsp.dir/build.make:169: recipe for target 'userspace/libsinsp/CMakeFiles/sinsp.dir/fdinfo.cpp.o' failed
make[2]: *** [userspace/libsinsp/CMakeFiles/sinsp.dir/fdinfo.cpp.o] Error 1
Merge pull request #212 from evgeni/fix-non-linux-build

fix building of libscap on archs w/o live capture support (*BSD, Hurd)
Merge pull request #213 from evgeni/fix-register_event_callback-ftbfs

fix build in register_event_callback after d5b334cebb96840885f6a5cd7557dd4672bfd931
Merge pull request #210 from ret2libc/master

improve json output
consolidated the protocol decoder callback types into a single enum
comment a currently unusued piece of syslog code
userspace/libsinsp: remove duplicated code
a bit more work on syslog decoding
userspace/libsinsp/filterchecks: make extract_as_js virtual
userspace/libsinsp/eventformatter: print ']' only if we have printed '['
more work on the syslog filtercheck. Still disabled.
more work on syslog decoding