TASK: zest, proxy: Implemented a ZEST interface (bug #10)

The ZEST interface may be short-lived if Yvan has a better zest.py
for me. The interface allows developers to import a list of HTTPRequest,
HTTPResponse pair and create a Zest scrit instance.

A new node called RawHeaders is added to the ProxyLogger interface (
i.e. added to the XML output that proxpy added) since ZEST requires
the string version of header be in the script. Instead of implementing
the string version ourselves, I am letting proxpy to export that str
to the XML file.
TASK: console: Create a console script to generate zest and requests. Fixed #11.

See also #4 and #6.