Markdown table generator

Turns tab- or comma-separated data into a markdown table with the columns padded so the source is readable, and tidies an existing table the same way.

Copying cells from a spreadsheet puts tab-separated text on the clipboard, which is why pasting straight in works. The padding is the part worth having: markdown does not require aligned columns and renders identically without them, but an unaligned table is close to unmaintainable in a text editor, and every table in a real repository is padded for that reason. The separator row is regenerated rather than preserved, so a table with a broken separator is fixed rather than reported — which is almost always what you want, since a broken separator means the table is not rendering at all.