Table-enforcer

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* Enforcer.recode lets Column.recode do the validation now
* Enforcer.validate no longer recodes
* Enforcer: make_validations now private
* Column: added find_failed_rows()
* columns now take series not dataframe
* added system-lvl tests based on Usage_Demo.ipynb
* Enforcer.recode create new df rather than copy
* added RecoderError and focused ValidationError
* remove testing for 3.5
* dont lint tests
* ignore flake8:W292
* formatting

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* Added tests for imports and more Class behavior
* main_classes: calling recode with validate is now prefered

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* main_classes.py: removed faulty imports

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* corrected Usage_Demo.ipynb
* formatting and typing
* table_enforcer.py -> main_classes.py

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* flake8
* set up basic testing
* changed travis build settings
* updated usage demo and readme

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* Added usage notebook link to docs.
* reorganized import strategy of Enforcer/Column objs
* added more builtin validators/recoders/decorators
* updated reqs
* initialized travis integration
* updated docs
* Added usage demo notebook for docs
* updated ignore patterns
* validators.py: renamed