Merge branch 'release0.3.9' into develop
Updated overall header comments.

* Removed "Author:"" tag. Let's use 'git blame' for that purpose.
* Updated copyright 2012 -> 2013.
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'