Fix example on Python 3

Actually, this in not a real fix. The problem is deeper.
`Redirector` doesn't properly handle exceptions, which raise between
`start` and `stop` calls.

So better is to replace current redirector with new one, which supports
context manager API (see issue #30)
Fix example on Python 3

Commented out check in `PyDSTool\Model.py` needs to be investigated
deeper. See comment in code and discussion in issue #29.
Fix Dopri/Radau compilation for Clang
Doc Clang support

[ci skip]