Fastcdc

Fixed
- maobaolong: fixed logic for ceiling division function; results of
chunking remain unchanged, so no visible difference.

Changed
- Add `build.rs` to generate the `table.rs` at build time, as needed.
- Add more documentation and a brief example of using `FastCDC`.

Added
- Added an example that processes files and computes SHA256 checksums.
- Added API documentation.

Changed
- Initial release