Adding some charsets

Newer versions of MySQL have more UTF-8 collations in addition to the
new utf8_mb4 charset/collation.

For some additional information about utf8_mb4, please refer to
http://dev.mysql.com/doc/refman/5.5/en/charset-unicode-utf8mb4.html
Merge pull request #124 from oliveiraev/fix-pymysql-charset

Adding some charsets