Zboxfs

This release is a API and binary incompatible release. Some major refactoring have been done in storage and transaction control.

- Added WebAssembly support
- Added zbox storage support
- Introduced LSMT (Log Structured Merge Tree) as index manager for file and zbox storage
- In storage interface, WAL IO is separated from data IO
- Added Node.js binding
- Removed external LZ4 dependency
- Many other minor bug fixes and performance improvements

In this release,

- Several bugs found in fuzz test have been fixed
- Some missing FFI parts are completed
- Two new docker images are created for building Zbox

This release is a binary incompatible release. There are some major changes have been done for volume, storage and transaction control.

- Memory and file storage module have been rewritten, storage interface has been redesigned to be able to support more types of storage in the future
- Volume module has been refactored, block and address cache are implemented in this module now, transaction operations are completed removed from volume and storage
- Trans module has been rewritten, introduced `Armor` trait, `Wal` and `WalQueue` object
- Fuzz test has been greatly simplified, now only one file can do all the fuzz test
- New `faulty` storage is developed to support random IO error test, which is integrated with fuzz test
- Compress is now optional and is disabled by default
- Add a new `dedup_chunk` option to `Repo` and `File`, which can turn on/off the data chunk deduplication
- Performance has been greatly improved due to the new volume and storage architecture design
- Many other minor bug fixes

In this release, some major changes are done for behaviors of read/write and rename on `File`. In general, their behaviors are more like normal file operations.

- Read/write will now affect the file position as normal Unix file operations will do
- Read will always perform on the latest file version
- Rename now behaves like [rename(2)](http://man7.org/linux/man-pages/man2/rename.2.html)

In this release FFI interface is added, and provided C/C++ binding as the initial stage. In the future, more language binding will be added based on this FFI. Also, fixed some minor bugs.

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

In this release,

- Add version_limit option to RepoOpener, which is the default settings for maximum number of file versions
- Some repo and fs code refactoring