Adding 3 more functions to svn: propdel(), propget() and propset() and some smaller changes

[BrunoBuett]

• added 3 svn functions in common.py: propdel, propget and propset

• added revision parameter in properties function

• added raw parameter for diff function

• added new test case for properties

-fixed unittest problems on Windows where path strings did not match due to different possible representations by adding a normpath2 function that unifies the paths on Windows

• updated README.md to cover changes and sorting function docs alphabetically

Please review the changes and if you are OK with it take it over. Thanks.