Fix #60: publish.py fails if IPython not installed

This fix just surrounds the import statement in __init__.py with try
except. This prevents publish.py from being imported of IPython is not
present.
Python3 compatibility

This commit fixes two compatibility issues. In setup.py execfile was
changed to support Python3 and in __init__.py the imports are now
relativ to support the changes made to the import system in Python3.