doc: use @rst/@endrst for ReST in headers

Folks found the use of @rststar/@endrststar non-intuitive (wanted to use
@rststart).  The "star" was there indicating the doxygen comment lines
had a leading asterisk that needed to be stripped, but since our
commenting convention is to use the leading asterisk on continuation
lines, the leading asterisk is always there.  So, change the doxygen
alias to the more expected @rst/@endrst.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>