Added charset support to utf8mb4.
Decode string in result for utf8mb4.
Add unsigned integer support.

Signed-off-by: Xiaolan.Lee <leexiaolan@gmail.com>
Removed incorrect assertion
Merge pull request #39 from LeeXiaolan/master

Add unsigned integer support.
Added test case utf8mb4 insert and retrieve.
Merge pull request #38 from Leechael/master

Added charset support to utf8mb4.
Merge pull request #1 from esnme/master

merge from upstream