v0.3.0 - Auto HTTP Exceptions & Open Timeout WS

Changes

• proxy_pass now raises HTTPException for 502 (Bad Gateway) and 504 (Gateway Timeout) automatically.
• Added customizable timeout to proxy_pass (HTTP) and open_timeout to proxy_pass_websocket (WS).~
• Added examples/02_http_errors demonstrating the exception.
• Fixed __init__.py to include Proxy() class.
• Updated README