Miscellaneous Regressions

[whatever]

Implement the three remaining regressions (currently uncategorized):

• coxph
• Arima
• eiRxC

Note that all three of these have unique setx methods.

[whatever]

coxph has been added, though it is in rough shape. In particular:

• a summarize.cox.ph method should be written
• setx.cox.ph may need to be implemented
• the code is extremely frail to various types of formulae that are non standard
• cluster(...) cannot be explicitly added

These issues are inherited from Zelig 3.5

[whatever]

Beginning work on Arima