fix httprunner#155: XSS in Jinja2 rendering

bugfix: when variable reference in testcase name is extracted from fo…

…rmer testcase, exception will occur

fix httprunner#131: parameter data driven with pair keys

bugfix: uniform response time unit to miliseconds

encode request data if it is in unicode/str type

print python 2 retire message as warning

refactor compatibility, learned from requests

refactor: load csv file with csv.DictReader

Prettify JSON testset format

Validate JSON testset format