Optimize build script

[shinenelson]

The build script was dependent on the directory in which it was triggered. This could cause inconsistency if the script was triggered from outside it's own directory.

The global variables allows the script to run with respect to the root of the repository allowing more flexibility, stability and consistency.

Also, there were multiple mv commands that could be merged into a single command.

[alexgibson]

/cc @m4rc1e

[m4rc1e]

@shinenelson thank you for the pr. I'll do a quick review.