Support macrons.

- Convert romaji with macrons to katakana with chō'onpu (長音符).
- Convert katakana with chō'onpu to romaji with macrons.
- Group macron tests in separate test file.
- Add macron tests to `package.json`.
Add missing `var` keywords.

My JS ninja scrolls tell me it's important to have these around.
Merge pull request #5 from modocache/macrons

Support macrons.