…ues:

* Previous headings for single settings were accidentally being included in the document before the start of a settings table. E.g. Browse Mode -> Maximum line length (which has no keyboard shortcut, was being included before Use Screen layout). This therefore also broke the Browse Mode table in to smaller tables.
* Tables were not being correctly ended with a blank line as markdown requires, so sometimes subsequent headings were being shown as raw markdown as part of the previous table. e.g. The Synth settings ring heading was being shown as raw markdown within the Synthesizer Selection table.

Also correct 0-based heading level counting: the first heading symbol in t2t is of length 1, but in markdown it is of length 2.
this stops the "Introduction" heading from accidentally appearing at the top of the key commands doc.