add regex exclude on jar assembly

[tolitius]

when building a jar with namespaces aot compiled:

$ clj -e "(compile 'yang.java)"; clj -A:jar

it does work, but also brings these along:

     0 Mon Aug 24 18:45:40 EDT 2020 clojure/core/
     0 Mon Aug 24 18:45:40 EDT 2020 clojure/core/specs/
   932 Mon Aug 24 18:45:39 EDT 2020 clojure/core/specs/alpha$fn__40.class
  1178 Mon Aug 24 18:45:39 EDT 2020 clojure/core/specs/alpha$fn__65$fn__71.class
   798 Mon Aug 24 18:45:39 EDT 2020 clojure/core/specs/alpha$fn__46.class
   929 Mon Aug 24 18:45:39 EDT 2020 clojure/core/specs/alpha$fn__27.class
   936 Mon Aug 24 18:45:39 EDT 2020 clojure/core/specs/alpha$fn__101.class
   929 Mon Aug 24 18:45:39 EDT 2020 clojure/core/specs/alpha$fn__25.class
   ...

this is due to the fact that "Clojure core uses specs for language features (as macros), so those get dragged in".

currently the only way not to have them in the jar is to manually remove them after the jar is built.

would be great to have a regex exclude option on jar assembly.