Docs: fix float value with old data

Signed-off-by: John Thornton <jthornton@gnipsel.com>
Docs: try to word synopsis to be a bit clearer in the description

Signed-off-by: John Thornton <jthornton@gnipsel.com>
pncconf -fix an icompatibility between MESA XMLs and linuxcnc XMLs

Linuxcnc used '???' to designate no secondary function, just GPIO,
where MESA use 'not used'. now both work
This made some GPIO pind not show in pncconf
Merge branch 'v2.5_branch' into 2.6