load path before starter-kit up and check loadable

  Place the full expansion of the load path at the beginning of the
  starter-kit start up.  Also, adds a function to check if a package may
  be loaded from source
move function definition before first use
no package-install if source is available locally

  This commit updates all places where packages are automatically
  installed using ELPA to first check if the package is available from a
  local source directory (i.e., under the src/ directory).  This makes
  it possible for users to override the ELPA versions of packages with
  local versions from source.  E.g., with this change I'm able to run my
  own fork of magit and starter-kit-misc.org will not install magit from
  ELPA.
remove marmalade and tromey from package-archives

  see issue 47
splitting yasnippet into starter-kit-yasnippet.org

  This way yasnippet may be optionally loaded, but is not required by
  default.
better installation of missing packages

  Consolidated some repeated logic into `starter-kit-install-if-needed'.
bringing back marmalade

  and in less than a day it's back, looks like there are some packages
  required by extra starter-kit files which are only in marmalade.
Modularize starter-kit-yasnippet
don't add ~/.emacs.d/ to load-path user src subdir

Very new versions of Emacs now complain about adding the base of the
~/.emacs.d/ directory to the load path.  Since the starter-kit suggests
placing source files into ~/.emacs.d/src/ instead of directly in
~/.emacs.d/, we may as well remove ~/.emacs.d/ from the load path as the
new Emacs warnings recommend.

I apologize if this change breaks anyone's existing config, although it
should be an easy fix, simply move all required .el files into the src/
subdirectory.