Initial import of indigena-rx

Imported code, fixed namespaces and adusted one test for changes since
0.14.1.
Replace chain with operators. General core cleanup
Got rid of base. It was weird.
Clean up future stuff and docs
Some more core operators
Update blocking stuff
Experimental warnings
Update Clojure README
fix gradle spec in README

presumably the group ID should be the same for gradle as for the other dependency managers.
Cleaned up naming of observable operator definition fns
Implement catch-error-value

Automating "rx.exceptions.OnErrorThrowable/addValueAsLastCause" idiom
when user code is invoked in onNext. Other minor cleanup.
more README
Implement group-by

Note that since 02ccc4d727a9297f14219549208757c6e0efce2a, the val-fn
variant of groupBy is unimplemented so for now an exception is thrown if
it's used.
Implement interleave and interleave*
Implemented partition-all

There isn't really an rxjava impl equivalent to clojure.core/partition,
so it's omitted.
Avoid intermediate toList for blocking/into
Update merge/merge-delay-error impls.

Split merge into merge/merge* for consistency with other functions that
can take one or more observables or observable of observables.
Updates from @mbossenbroek's feedback.
interpose docstring
Reimplement into without toList