hotfix: v0.5.1 fix iss#23

Document.add_picture() raises ValueError when document contains VML
drawing
docs: document feature analysis for Run.style
acpt: add run-char-style.feature

Acceptance tests for character style support, implemented as the
read/write Run.style property.
run: add Run.style getter
run: add Run.style setter
acpt: add par-add-run.feature

Retroactively added an acceptance test for Paragraph.add_run(). Made
some stylistic updates to naming in steps along the way.
run: add style param to Paragraph.add_run()
docs: add user documentation for Run.style
release: v0.5.2 #17 feature: character style
docs: document Run.underline feature analysis
acpt: add run-enum-props.feature

Add scenario outline to test Run.underline getter at API level.
run: add Run.underline getter
acpt: add scenario for Run.underline setter
run: add Run.underline setter
release: v0.5.3 add feature #19 Run.underline
Merge remote-tracking branch 'origin'

Conflicts:
	docx/enum/text.py
	tests/test_text.py