Using coverage and coveralls.io.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Add badges of travis-ci, version to README.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Merge pull request #4 from mkouhei/apply_coverall

Apply coverall and add status badges.