Fix typos.
Fix .gitignore.

Use /rgl instead of rgl/ to ignore only the top-level /rgl directory.
Remove 'rescue LoadError'.
Require test_helper in all tests.
Remove commented code.
Extract helper classes into separate files. Add script/test_all.

Extract GraphIterator, GraphVisitor, and GraphWrapper from traversal.rb
into separate files so they can be used elsewhere without requiring
traversal feature.

Fix requires in the source and test files.

Add script/test_all that run all tests together and then one by one (to
detect missing requires in the test).
Use script/test_all on Travis CI.
Use 'alias' with methods and not symbols (for consistency).
Remove "require 'rubygems'" statements.

Requiring 'rubygems' inside a gem is considered to be a bad practice.
Here's why: http://tomayko.com/writings/require-rubygems-antipattern.
Require rubygems in test_helper (for MRI 1.8.7).
Refactor GraphVisitor.

* Make def_event_handler available wherever GraphVisitor is included.
* Accept symbols in def_event_handler.
* Extract distance map support into a module.
Remove JRuby from Travis CI build.

JRuby support is tricky, because of the dependency on 'algorithms'
gem that includes C extensions and the fact that building native
extensions for JRuby is not recommended and most likely will become
impossible in the future.
Add Dijkstra algorithm.
Add Graph#dijkstra_shortest_paths method.
Rename internal DijkstraQueue class to Queueu. Add comments.
Skip finished vertices in Dijkstra edges relaxing loop.
Add visitor test for Dijkstra algorithm.
Merge pull request #5 from KL-7/dijkstra

Add Dijkstra shortest path algorithm.