MODE-1753 Merge two README files into one

Simple-minded merge:
 * copy the information from the README_COMMITTERS.txt file and insert
   into appropriate place in the README.md file
 * remove the README_COMMITTERS.txt file
MODE-1753 Removed "pardon our dust" from the 3.0 beta days

The top of the README.md file contained out-dated information from when
the 3.0 work had first moved to the master branch. Zapped it.
Merge branch 'MODE-1753' of git://github.com/jstansel/modeshape into jstansel-MODE-1753