tablature harmonic and slides index entries

[Federico Bruni]

In notation/fretted-strings.itely there are the following index entries:

##################################################################
@cindex harmonic indications in tablature notation
@cindex tablature and harmonic indications
@cindex slides in tablature notation
@cindex tablature and slides
@cindex chord glissandi
@funindex \harmonic
@funindex \harmonicByFret
@funindex \harmonicByRatio

Harmonic indications can be added to tablature notation as sounding
pitches:
##################################################################

However, in the Notation index harmonicByFret and harmonicByRatio have 
only links to available music functions. Why it's missing a link to 
chapter 2.4.1 (where the full explanation of these commands can be found)?

Please also move the following index entries down where they should 
stay, close to the slides-in-tablature and chord-glissando-in-tablature 
snippets (from line 447):

@cindex slides in tablature notation
@cindex tablature and slides

@cindex chord glissandi

Thanks,
Federico