fix compatibility for python 3.4, 3.5

bugfix: make compatible with download api that response in bytes

update setup.py

call load_dot_env_file when initializing HttpRunner

bugfix httprunner#210: SuiteNotFound

release 1.4.0

merge_validator: support checking unhashable values such as dict

fix httprunner#188: display response image in html report

filter output if out is empty

fix httprunner#155: XSS in Jinja2 rendering