Merge branch 'switchd_branching' into develop
Migrated base files from apps/topology
Add show_switch_status command
* Moved show_{topology,switch_status} to examples/topology
* Minimized show_topology example
* Add sample .conf file
* Add external attribute to show_switch output.
Refactor and merge apps/topology to trema.
Rename libtopology -> topology.  C API part for #3.
Add event filter operation. (#2)
I compile step definition should build in trema C compatible options.
Auto start topology daemon. (#5)