Add required_ruby_version to gemspec

This specifies that Trema is compatible only with Ruby 1.8.7. This way
nobody will get confused if they're using 1.7 or 1.9 family.
Version bump to 0.3.10
Merge branch 'release0.3.10' into develop
Make PacketIn#initialize_copy private (refs #218)
Refactoring trema.gemspec

- Explicitly specify that Trema is only for Linux.
- Remove redundant dependencies.
Updated :development gem bundle.
Updated code climate badge
Updated StatsReply#stats YARD comment (Thanks Tomizawa-san).
Fix ARGV passed to Ruby controller
Version bump to 0.3.11
Merge branch 'release0.3.11' into develop
Upgrade flay to the latest version
Version bump to 0.3.12
Merge branch 'release0.3.12' into develop
Merge branch 'develop' into topo-trema-C
Merge branch 'topo-trema-C' into topo-trema-Ruby