Improve regexp input(#1)

Some regexp, such as '^class,' is not worked in original code.
Because beginning of candidate is line number, not buffer content.
So I fix it to use 'get-line' helm attribute.

And add 'filtered-candidate-transformer' for highlighting
regexp input.

This is screenshot.
![helm-swoop](https://f.cloud.github.com/assets/554281/1443456/4f20f9ee-41e5-11e3-8028-bb3acfc65b67.png)

Please see this patch.