add .eaf parser (#37)

* add original eaf parsing text

* set up basis of eaf parser

* set up test for eaf parser

* start eaf parser with a loop

* parser works in loop

* fix flake8 issue with etree import

* reduce hardcoding by assigning variables at the top of the class

* refactor parser

* deal with annotations with matching time slots

* rewrite elan parser with pympi-ling dependency

* add metadata extraction

* wrap eaf parser

* allow tier selection

* add docstrings to import methds

* noqa for linter error

* add conversation properties

* add selection and summary functionality

* allow user to remove data based on fields

* address linter complaint

* update example notebook in docs

* added check for empty list and autopep8 fixes

* add pympi_eaf attribute on init

* Update sktalk/corpus/parsing/eaf.py

Co-authored-by: Carsten Schnober <carschno@users.noreply.github.com>

* Update sktalk/corpus/conversation.py

Co-authored-by: Carsten Schnober <carschno@users.noreply.github.com>

* Update sktalk/corpus/conversation.py

Co-authored-by: Carsten Schnober <carschno@users.noreply.github.com>

* rewrite utterance extractor to reduce indentation

* update tests to reflect __len__

* add docstring with error and warning info

* rename kwargs to fields and autopep8

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Co-authored-by: Carsten Schnober <carschno@users.noreply.github.com>