Improve markdown generation of tabular content

[sbs-jms]

While working with the Swordfish spec, I found a number of cases where the generated markdown required additional hand editing, including :

• adjusting column widths for different table types
• adding blank lines to isolate paragraph text for bulleted lists
• adding blank lines to separate header text from body text
• removing intra-cell whitespace, to minimize text wrapping
• adding blank line to separate table from caption