TiKV release v5.1.0

Bump version to 0.3.0.

Bump version to 0.2.2

add keywords

Remove unstable features for 1.1 compatibility.

Multithreading support, fixes for memory leaks.

Snapshot, iterator, and comparator support.

WriteBatch support, fixes for memory leaks.

Merge pull request #8 from spacejam/nightly_6.28.15

Nightly 6.28.15 update.