Generate shebang in amberc
Fixes #630 even better.

npm "bin" has nice wrapper over node files
(with #/ust/bin/env node shebang), so both amber and amberc
(wrapping bin/amber-cli.js and bin/amberc)
are made so they are in this format for npm.

bin/amber and bin/amber.bat are useless for npom deployment,
they are there to have something callable as 'bin/amber'.