initial commit
Add xml layer with support of various ElementTree-based XML modules.

By default, modules are prefered in next order:
- lxml.etree
- stdlib xml.etree.cElementTree and xml.etree.ElementTree (Py2.5+)
- external cElementTree and elementtree.ElementTree
Add mapping module to contruct data messages in object-like way.

This module helps to create schema-strict messages and provides abstraction
layer from data protocol. It implements all used fields types of LIS server:
boolean, integer, long, float, reference, text, datetime, list and object.

Based on couchdb-python mapping module.
constants module was very bad idea
implement basic tests runner
fix typos
add http module heavily based on couchdb-python project same one.
force wrap data by content tag for Message's
add base LIS server exceptions.
description may be omitted for error messages
respect to authors of original module
add base messages to build requests and wrap responses
remove useless imports
phox response messages has no type attribute
rename session_id to sessionid to simplify arguments automapping
initial client with implemented authentication support
simplify Mapping.wrap logic:

- remove dict support
- since data fields couldn't be on document root level, there is no
needs to have specific branch for xml element processing.
make wrap/unwrap routine common for all phox response messages
request message data are always wrapped by content tag
move Message class to messages.py module