Add acceptance test for paragraph alignment
Add PpParagraphAlignment constants
Add alignment property to _Paragraph
Add ParagraphAlignment.to_text_align_type()
Add ParagraphAlignment.from_text_align_type()
Add test data for paragraph object
Implement CT_TextParagraph
Clean up logging
Add acceptance test for cell vertical anchor
Add vertical_anchor property to _Cell
Implement spec.VerticalAnchor value mapper
Implement anchor property on CT_TableCell
Add acceptance test for cell margins
Implement bottom_margin property on _Cell
Implement marB property on CT_TableCell
Implement remaining margin properties on _Cell

* reorder acceptance test margin calls to respect top, right, bottom,
left sequence convention (start at top, proceed clockwise)
* generalize margin unit tests to cover all four margin settings with
each of three tests
Implement marX properties on CT_TableCell

* generalize test cases to cover all marX attributes
* generalize setter to work for all marX attributes
* factor out guts of getter into _get_marX(), leave the individual
getters as properties so it's not abstracted past the point of easy
understanding
* establish developer documentation for pptx.oxml
Document analysis of table boolean properties
Add acceptance test for _Table.first_col property
Implement first_col property on _Table