Fix the mixing of `self.arguement` and `argument` 

Patch to fix the mixing of `self.arguement` and `argument` usage in `__init__` that causes an error if the user does not set the `eTime` optional argument.

Also, fixed mixing of `self.sTime` and `sTime` since that may also cause problems that haven't been found yet.
Merge pull request #6 from asreimer/patch-16

Fix the mixing of `self.arguement` and `argument`