Add `--force-yes`

Sometimes there are problems:

WARNING: The following packages cannot be authenticated!
         debhelper
E: There are problems and -y was used without --force-yes
Merge pull request #4 from wless1/master

Set LIBRARY_PATH for compile-time linking
Merge pull request #1 from gjtorikian/patch-1

Add `--force-yes`
emits PKG_CONFIG_PATH; forces re-installation of each explicitly listed package in Aptfile

- avoid `-fPIC` disparity i.e. libvips (Aptfile) + libpango (Cedar 14)

  pkg-config
  libpango-1.0-0
  libpangocairo-1.0-0
  libpangoft2-1.0-0
  libvips-dev
  glib2-dev
  ghostscript
patches LIBRARY_PATH, LD_LIBRARY_PATH to also support i386 / x86_64 specific binaries
adds platform-agnostic variant to PKG_CONFIG_PATH
Merge pull request #6 from evadne/feature/pkg-config

libVips / slugbuilder support
Fix up envvar exports for the apt buildpack.

 * Avoid adding extra : characters to the end of gcc paths.  This will
 cause gcc to use the current directory in system include paths, which
 breaks C #include <file> vs #include "file" semantics.
 * Also, write an export file for buildpack-multi to pass the exported
 envvars to the next buildpack.
Make this bit agree with bp locations again
fix typo in bin/compile
Merge pull request #7 from rdio/dokku-wip

Fix up envvar exports for the apt buildpack -- fixes C/C++ compiling.
Merge pull request #8 from sjansen/patch-1

fix typo in bin/compile
Allow to specify remote deb packages on Aptfile

Closes #9