dynamic value creation inside bxb files

https://stackoverflow.com/questions/57246518/how-can-i-dynamically-pull-version-from-git-into-capsule-bxb

I want to be able to create my version number in capsule.bxb by pulling dynamically from git as described in the post above.  this could be accomplished by providing a facility for bxb files to make dynamic queries, or (maybe simpler) by allowing bxb files to read from files/environment variables.