Issue 3694: Use standard inclusion scheme for FreeType headers.

The most recent FreeType release (2.5.1) has changed locations for header
files.  Using the standard way, this is not visible to applications.
Doc-es: update Changes, Engraving, Common, Fundamental, Tutorial.
Fix node names and translationof statements.
Doc-es: update Tweaks, Chords, Ancient.
Doc-es: update Programming interface, Changing defaults, Editorial.
Doc-es: update Fretted, Input, Keyboards, Percussion.
Doc-es: update Rhythms, Simultaneous, Spacing, Staff, Vocal.
Doc-es: update Usage/External, Running, Updating.
Web-es: update NEWS.
Doc-es: fix some node names.
Web-es: update Download.
Doc-es: small reword in translation of Keyboards.
Doc-es: add translations of new snippets.
Doc-es: translate remaining snippets, phase one.
Doc-es: nits in Spanish snippets.
Doc-it: spell-check all the files translated so far

Add also minor updates and missing translations.
Doc-it: add Changes page
Doc-it: update old node name and delete wrong translation
Doc-fr: get rid of @c LocalWords left by Aspell
Doc-es: translate remaining snippets, phase two.