Make dependencies optional

[HDembinski]

Some people like myself are not interested in the API that requires scipy or algopy. Please make these dependencies optional.

[pbrod]

Ok, I can do that in the next release.

[pbrod]

Just note that scipy is not optional!
Only
algopy
statsmodels
matplotlib
can be made optional

[pbrod]

Closing this issue as it is resolved in release 0.9.42