Python-box

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* Adding support for list traversal with `box_dots` (thanks to Lei)
* Adding `BoxWarning` class to allow for the clean suppression of warnings
* Fixing default_box_attr to accept items that evaluate to `None` (thanks to Wenbo Zhao and Yordan Ivanov)
* Fixing `BoxList` to properly send internal box options down into new lists
* Fixing issues with conversion and camel killer boxes not being set properly on insert
* Changing default_box to set objects in box on lookup
* Changing `camel_killer` to convert items on insert, which will change the keys when converted back to dict unlike before
* Fallback to `PyYAML` if `ruamel.yaml` is not detected (thanks to wim glenn)
* Removing official support for `pypy` as it's pickling behavior is not the same as CPython
* Removing internal __box_heritage as it was no longer needed due to behavior update

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* Fixing `get` to return None when not using default box (thanks to Jeremiah Lowin)

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* Fixing non-string keys breaking when box_dots is enabled (thanks to Marcelo Huerta)

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* Fixing converters to properly pass through new box arguments (thanks to Marcelo Huerta)

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* Fixing setup.py for release
* Fixing documentation link

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* Adding support for retrieving items via dot notation in keys
* Adding `box_from_file` helper function
* Adding merge_update that acts like previous Box magic update
* Adding support to `+` boxes together
* Adding default_box now can support expanding on `None` placeholders (thanks to Harun Tuncay and Jeremiah Lowin)
* Adding ability to recast specified fields (thanks to Steven McGrath)
* Adding to_csv and from_csv capability for BoxList objects (thanks to Jiuli Gao)
* Changing layout of project to be more object specific
* Changing update to act like normal dict update
* Changing to 120 line character limit
* Changing how `safe_attr` handles unsafe characters
* Changing all exceptions to be bases of BoxError so can always be caught with that base exception
* Changing delete to also access converted keys (thanks to iordanivanov)
* Changing from `PyYAML` to `ruamel.yaml` as default yaml import, aka yaml version default is 1.2 instead of 1.1
* Removing `ordered_box` as Python 3.6+ is ordered by default
* Removing `BoxObject` in favor of it being another module