Update Base64 to modern Java

[cloojure]

Works with Clojure 1.8/1.10.1 and Java 8/12

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lein test flatland._bootstrap

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   Clojure 1.10.1    Java 12
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lein test flatland.useful.bean-test

lein test flatland.useful.cli-test

lein test flatland.useful.compress-test

lein test flatland.useful.config-test

lein test flatland.useful.datatypes-test

lein test flatland.useful.debug-test

lein test flatland.useful.deftype-test

lein test flatland.useful.dispatch-test

lein test flatland.useful.exception-test

lein test flatland.useful.experimental-test

lein test flatland.useful.fn-test

lein test flatland.useful.io-test

lein test flatland.useful.java-test
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by flatland.useful.java$invoke_private to method java.util.Hashtable.rehash()
WARNING: Please consider reporting this to the maintainers of flatland.useful.java$invoke_private
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

lein test flatland.useful.macro-test

lein test flatland.useful.map-test

lein test flatland.useful.ns-test

lein test flatland.useful.parallel-test

lein test flatland.useful.seq-test

lein test flatland.useful.state-test

lein test flatland.useful.string-test

lein test flatland.useful.test-test

lein test flatland.useful.utils-test

Ran 143 tests containing 546 assertions.
0 failures, 0 errors.
lein test :all  18.45s user 0.47s system 302% cpu 6.247 total