spec: fix iss39 add x-fontdata part type
setup: require lxml >= 2.3.2
accept: add auto-create features/_scratch/ directory
hotfix: Windows requires 'b' in file open mode

Renamed parameter 'file' to 'file_' where it occurred. Lack of 'b' in
open() calls produced multiple test failures. No production code was
impacted.
fixed up all commits on wordwrap feature, added behave tests as well
const: migrate CONTENT_TYPE to opc_constants.py
const: migrate RELATIONSHIP_TYPE to opc_constants
oxml: refactor namespace prefixed tag handling
test: refactor to use assertEqualLineByLine
iss36: remove indiscriminate deannotation
opc: remove pretty-print of saved XML
test: add [pytest] section to tox.ini
refactor: rename file to file_ in open() methods

'file' is a reserved word. Appending underscore to reserved words to
form a variable name is some sort of convention.
refactor: rename test/ to tests/
reorg: migrate text-related steps to own module
reorg: migrate table-related steps to own module
reorg: migrate placeholder-related steps to own module
reorg: migrate core props steps to own module
reorg: migrate picture-related steps to own module
reorg: migrate shape-related steps to own module