Remove unused files and set master branch to declare HPHP_VERSION==2.1.0-dev
Update folly
Add install target (and remove errant install targets from 3rd party)

make install
  Installs hhvm and systemlib.php to CMAKE_INSTALL_PREFIX/bin

To override the default location define it during cmake:
  cmake -DCMAKE_INSTALL_PREFIX=/usr/hphp .