Improved the speed of this macro.

It is not necessary anymore to use the arrow keys and a modifier. Instead just activate the macro and then press 1-6 on the keyboard. I'll add some documentation to the Wiki.
Fixed a bug that was causing this macro to misbehave

A miscalculation. Why did I not add the `=0` condition in previous versions? Who knows. It'll stay a mystery.
Collapsed some boxes
Added the feature back where you can "tab out of" the macro header.

This was the one case where the user was able to have no text selected and just start typing a header. This now also let's the user pick a header level by pressing 1-6.
Merge branch 'speed-up-header-macro'