docs: #' no longer needed with \tag, \removeWithTag, \keepWithTag

[Paul Morris]

In 2.17 you no longer need to use #' with \tag, \removeWithTag, or 
\keepWithTag.  This is a helpful simplification but it is not yet reflected in 
the docs.[1]  For example:

  \tag #'aa  % old way
  \tag aa     % new way

Dotted lists work too:

Instead of:
  \removeWithTag #'aa 
  \removeWithTag #'bb
  \removeWithTag #'cc
  \tag #'aa \tag #'bb \tag #'cc { g1 }

or:
  \removeWithTag #'(aa bb cc)
  \tag #'(aa bb cc) { g1 }

you can now just do this:
  \removeWithTag aa.bb.cc
  \tag aa.bb.cc { g1 }

I think it's also worth adding \tag to this list on the changes page[2]:
  Several commands now accept symbol lists (conveniently entered as 
dot-separated 
  words) for various kinds of arguments. These include ‘\accidentalStyle’, 
  ‘\alterBroken’, ‘\footnote’, ‘\hide’, ‘\omit’, ‘\overrideProperty’, ‘\shape’, 
  and ‘\tweak’.

[1] 
http://lilypond.org/doc/v2.17/Documentation/notation/different-editions-from-one-source#using-tags
[2] http://lilypond.org/doc/v2.17/Documentation/changes/index.html