Use lcov format

Trying to support [lcov format](http://ltp.sourceforge.net/coverage/lcov/geninfo.1.php) that is widely used among CI services. (ex. [Coveralls](https://coveralls.io/))

- [x] Add lcov example
- [x] Test
- [x] Implement
- [x] Refactor
- [x] Deprecate old CSV format