compilationConstants Implementation

[kaaninel]

Fixes #15

[paul-go]

• You can use String.repeat instead of a regex
• I don't think this needs to be async ... it's a build tool, I don't think non-blocking IO matters.
• There's some code formatting problems here, but I think you probably don't have ESLint setup properly.
• I think you've got whitespace trimming on your editor (looks like the .editorconfig isn't working)