copy regexp from MySQL-python 1.2.4

Fix #7
intergrate with pymysql>=0.6

pymysql 0.6 removed errorhandler and move init_commands etc from
Connection.__init__() to Connection._connect().
update pymysql version
require umysql>=2.61

umysql-2.61 returns datetime object directly, no conversion needed.
Fix issue #8

Django 1.6 has this import statement:

    from MySQLdb.converters import conversions, Thing2Literal

so we'd better support that.
Merge upstream changes for better compat with pymysql 0.6