Web: nitpicks in Intro & Manuals, mostly typography and spelling

Web: nitpicks in Intro & Manuals, mostly typography and spelling

- Internals in PDF and Info formats also have clickable links,
- remove redundant copyright notice (alreaady defined in macros),
- replace '...' with @dots{},
- two spaces after the end of a sentence,
- comments for translators,
- spelling mistakes,
- a couple of wrong xref macros,
- last xml2ly is seven years old and outputs for Lily 1.x,
- a few other nits.