fix ach file generating

Hello.

I have some fixes:

- Comment from Bank Technical Specialist "The effective date must be at least one business day later than the file creation date". Added possibility to pass custom `eff_ent_date` to `AchFile.add_batch`.
- Fixed Entry Hash. Should be "Sum of first eight digits of the routing-transit 
numbers within the batch". Looks like you have added check digit and forgot to fix `get_entry_hash`.
- Sum of amounts should be equal in `BatchControl` and `FileControl`. All amounts already fixed here https://github.com/travishathaway/python-ach/blob/master/ach/builder.py#L88, no need to do this in `FileControl`.
- You should not use mutable object as default value for function arguments. http://effbot.org/zone/default-values.htm

File generated with these fixes was validated by ACHViewer.