add PBB support
fix MPLS operations

* make parse_mpls parse multiple mpls shims
* make use of mpls_header_t
* mpls push tag sets ethertype
* fix unittests to use new packet_info members
fix warnings

`rake run_unitttests` stops because of -Werror
add comment in unused unittest
fix warnings

`rake run_unitttests` stops because of -Werror
add comment in unused unittest
add PBB support
fix MPLS operations

* make parse_mpls parse multiple mpls shims
* make use of mpls_header_t
* mpls push tag sets ethertype
* fix unittests to use new packet_info members
Merge branches 'pbb_and_mpls' and 'pbb_and_mpls' of https://github.com/iHiroakiKawai/trema-edge into pbb_and_mpls
Merge branches 'fix_unittests' and 'fix_unittests' of https://github.com/iHiroakiKawai/trema-edge into fix_unittests
Merge pull request #76 from iHiroakiKawai/fix_unittests

Fix unittests
Merge branch 'pbb_and_mpls' of https://github.com/iHiroakiKawai/trema-edge into iHiroakiKawai-pbb_and_mpls
update comment
update src/examples and README