Ruby 1.8 and YARD legacy mode compatibility

NamespaceResolver uses a different method for locating the statement's
enclosing namespace since statements are not AstNodes in the legacy
parser.

Built a Legacy appendix handler with its own specs and stubs. Also,
added ruby1.8 env to travis-ci builds.
Merge branch 'master' of github.com:amireh/yard-appendix

Conflicts:
	lib/yard-appendix/version.rb