Improve response to pilot down command

Changed the keep-alive command for the containers so they should stop immediately instead of taking 10 seconds to respond.

Some bugfixes and enchancements

• use PHP built-in web server for local development server (pilot serve accepts the same arguments as php -S
• BUILD_COMMAND environment variable to customise what it is run for php build
• fixed bug where NODE_SERVICE was not defaulting to MAIN_SERVICE
• fixed bug with npm commands incorrectly accessing NODE_SERVICE variable

0.1 - Initial release

- added license and readme