Parse content from a stream.

Here is the initial code for parsing content from a stream.

When writing tests I find it much easier (and faster) pass StringIO
instead of writing content on a real disk.

This branch add initial support for that.

I have updated LessLexer.input() to allow both a stream and a path, since yacc API is ugly.

I have not updated LexxLexer.file() method since I have no idea how and where it is used.

Let me know if you find it useful or would like some changes or feel free to reject it.

I agree that most unit test should be written at a lower level, but first time when I look at the code, I find it easier to have these integration tests and see how things are coupled.

Also the unit test suite is very slow so I hope that its speed can be improved by writing more targeted integration tests.

Testing whole bootstrap project is nice but I don't think that this should be included in the continuous integration system.

Sorry for all the noise with py3 support. I am new to py3 development but I will install tox and run the tests.
Thanks!