* Documentation/user/introduction.itely (Computerized typography):

* Documentation/user/introduction.itely (Computerized typography):
new section

* Documentation/user/tutorial.itely (An orchestral part): remove
pc example from tutorial.

* input/tutorial/lilbook.tex: use screech-boink

* scripts/lilypond-book.py (compile_all_files): split formatting
output body and scheduling lilypond compilation.
(format_lilypond_output_bodies): new function
(format_lilypond_block): new function
(html_pages): allow multi-page images in HTML

* python/lilylib.py (make_ps_images): rename function from
make_preview, merge with make_page_images