Doc: organize changes.tely

[Jean-Charles Malahieude]

Hi all,

Purging the French version of changes.tely, came to my mind it might be 
wise to avoid moving around and re-organize items like James did in late 
2017 when preparing for a new major release (and translators afterwards) 
and have it structured on the fly. This was the first time for those 
News to be categorized, but I think it's worth it. For the record, here 
is James "sectioning":

*New for musical notation
 -Displaying pitch improvements
 -Rhythm improvements
 -Expressive mark improvements
 -Repeat notation improvements
 -Staff notation improvements
 -Editorial annotation improvements
 -Text formatting improvements
*New for specialist notation
 -Vocal music improvements
 -Unfretted and fretted string instrument improvements
 -Chord notation improvements
*New for input and output
 -Input structure improvements
 -Titles and header improvements
 -Input file improvements
 -Output improvements
 -MIDI improvements
 -Extracting music improvements
*New for spacing issues
 -Page breaking improvements
 -Vertical and Horizontal spacing improvements
*New for changing defaults
*New for Internal interfaces and functions

Cheers,
--
Jean-Charles