Merge 0.3.3 changes

0.3.3
-----

0.3.3 changes the way null values are handled, and introduces interface for CAS operations.
It is strongly advised that you upgrade to 0.3.3 since it contains important fixes.

- [PUT will not store null values](https://github.com/junegunn/hbase-jruby/issues/15)
- `filter(column: nil)` will match rows without the column
- `filter(column: value)` will *NOT* match rows without the column
  - However, `filter(column: { ne: value })` *WILL* match rows without the column
- [Added `HBase::Table#check` method for check-and-put and check-and-delete operations](https://github.com/junegunn/hbase-jruby/issues/14)
  - `bool = table.check(1, in_print: false).delete(:price)`
  - `bool = table.check(1, in_print: true).put(price: 100)`
- Fix: invalid count when filter is used