Extend Inst protocol to org.joda.time.DateTime

[glts]

Clojure 1.9 introduced the Inst protocol and with it the predicate inst? and the accessor/conversion operation inst-ms.

Out of the box, Inst is extended to java.util.Date and, on Java 8 and later, to java.time.Instant.

(inst? (java.util.Date.))        ;; => true
(inst? (java.time.Instant/now))  ;; => true
(inst? (clj-time.core/now))      ;; => false

Please consider extending the Inst protocol to org.joda.time.DateTime on Clojure 1.9 and later. This would help improve interoperability and using insts more independently of the concrete implementation. Since clj-time in some sense has a de facto ‘ownership’ of org.joda.time.DateTime in the Clojure library world, I believe you are best suited to do such a protocol extension.

Thank you!

[seancorfield]

Sounds reasonable. PR, with tests, welcome.

Note: if you're on Java 8 or later, you should consider migrating from Joda Time/clj-time to Java Time (and, perhaps, clojure.java-time if you want a wrapper library).