Support adding clue/phar-composer as a require-dev and running out of vendor/bin

From a random project running

    php composer.phar require --dev clue/phar-composer
    php composer.phar update
    php composer.phar install

allows this

    ./vendor/bin/phar-composer

to work using a technique similar to the one used by phpunit.
Use STDERR for missing composer setup error + PSR2 code style
Merge branch 'pr/36'
Add PR 36 (support running from require-dev) to changelog
Avoid dev packages when building the phar

Presumably there should be --dev / --no-dev options in the future.
Actually exclude the vendor dir
Merge remote-tracking branches 'no-dev' and 'no-vendor'

* radford/no-dev:
  Avoid dev packages when building the phar

* radford/no-vendor:
  Actually exclude the vendor dir