update contributor guide, making clear a prototyping language cannot itself be build out of prototypes

Some gentle reformatting to make the Markdown more standards-compliant, so that it renders correctly on Github.

* Macports build instructions were incomplete. The main blocker was that
packages/darwin_app/embed-MacOSX-dependencies.sh is hard-coded to use
homebrew paths instead of Macports or Fink paths. That could be fixed,
but there are bigger problems:
a) having two build environments splits the developer knowledge-base in
half and potentially doubles the number of build issues
b) Macports requires full XCode which is multi-gigs of download and
probably hours more of installation time. In fact I ran out of space on
my OSX VM just from the App Store trying to update XCode!

Added Albert to the list of maintainers

These are needed to fetch ASIO SDK and nw.js binaries