Cleaned up README and converted to markdown
emacs-mac.rb: Emacs.app no longer default install to /Application but need a link build-emacs.app.sh issue #17
I misunderstood the formula syntax. depends_on 'libxml2' => [:optional, 'with-xml2'] will build the libxml2 dependency with the 'with-xml2' flag. What I wanted was to rename the 'with-libxml2' flag on the emacs-mac formula itself to 'with-xml2' (because emacs itself is using 'with-xml2'). Fixed in this commit (also for the 'with-dbus' flag).