docs: update README.mysql

1) add steps to import database.
2) add steps to install mysqldb in python.

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>
data: add 4 class methods

Added getOpen(), getClose(), getHighest(), getLowest().

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>
Merge branch 'winf-dev' into zhengwang-dev