Retrieve Boot's fake classpath.
When using Boot, fake.class.path contains the original directories with source
files, which makes it way more useful than the real classpath.
See https://github.com/boot-clj/boot/issues/249 for details.

Check whether we're dealing with a Boot project.
We figure this by checking for the presence of Boot's fake classpath.

Merge maps recursively. When vals are not maps, last value wins.

Transform a value for output

Update the keys of map `m` via the function `f`.

Update the values of map `m` via the function `f`.