Massaging the build process

Preparing ground for further work on build scripts.
See [BashGuide/Practices#1](http://mywiki.wooledge.org/BashGuide/Practices#Choose_Your_Shell). In the POSIX standard, naming a file with the `.sh` extension implies that the file is POSIX shell script, not bash. Since we can't predict how the end-user's shell will be configured, how the shebang will be interpreted becomes anyone's guess. It behooves us to stick to best practices here.