Snapshot of signatures from build

[wallymathieu]

Add all signatures during build in order to be able to get a diff of the signature differences when refactoring the project. The fsi-files are not included in the build, so should not affect the output.

• [ ] document that fsi files are snapshot of build results rather than source files
• [ ] include fsi files in the docs build in order to be able to view the changes between releases