ISSUE-86: tts:dynamicFlow - further simplifications - fade, within flow [DFXP 1.0]

ISSUE-86: tts:dynamicFlow - further simplifications - fade, within flow [DFXP 1.0]

http://www.w3.org/AudioVideo/TT/tracker/issues/86

Raised by: Glenn Adams
On product: DFXP 1.0

1. due to lack of specificity and expected lack of implementation, remove 'fade' flow style;
2. due to lack of expected use and lack of implementation, remove 'within()' flow function, i.e., have within() always follow out();

either or both of these functions could be restored in a subsequent revision of the specification, provided they are better specified (in the case of 'fade') and provided they are implemented;