Pigar

- Fixed [34](https://github.com/damnever/pigar/issues/34)

- Fixed the .egg suffix which caused by sudo pip install ... on Ubuntu.
- Workaround for special packages, such as [29](https://github.com/damnever/pigar/issues/34)

- Fixed [26](https://github.com/damnever/pigar/issues/26)
- Fixed relative import issue.

- Fixed ImportError.

- Supported flask extension.
- Sorted requirements.
- Use gevent if possible.

- If modules in the `try...except...` block, assume they are optional.