Zboxfs

This is a repository incompatible release, to upgrade to version all repository files need to be re-imported.

In this release,

- Virtual IO layer is introduced to FileStorage to support random IO error test
- Performance test and fuzz test are moved to integration test directory
- FileStorage entity map number reduced to 4 in order to improve performance

This is a bug fixing release, fixed several issues in document.

**Note**: This release is **NOT** repo binary compatible with v0.1.4.

In this release:
- Change content split to be on chunk boundary
- Segment can shrink now, this can dramatically reduce disk space waste
- Add merkle tree as content hashing algorithm, improve 60% file storage write performance
- Add performance test tool

- Add Windows support
- Improve and add data persistence for fuzz tools
- Fix several critical bugs in fnode and file storage
- Some other code improvements

This release is mainly for changing misleading term `zero-knowledge`. There also some other fixes and improvements.

- Fix issue in the sample code in README
- Add create_new() function to RepoOpener.

This is the initial release of `Zbox`.