The Kotlin version of Astronomy Engine was using Java
classes like `Date` and `GregorianCalendar`.
Reworked the code to use a completely self-contained
representation of calendar date/time, just like the C version does.
Now Astronomy Engine does not depend on anything outside of
the Kotlin standard library. This should allow us to use
Astronomy Engine for Kotlin Native apps, Web Assembly, etc.
Updated Java demo to use the new method Time.fromMillisecondsSince1970.
Moved the step that creates the fatJar into
the main build process for Kotlin. This is
needed to run the Java demos, and it is good
to fail early if it cannot be built.
Renamed AstroTime to Time.
Renamed AstroVector to Vector.
For some reason this breaks the Java demo build.
I'm pushing the broken build anyway to see if
ebraminio can help me fix it.
Restructured the Java code so we pass in command
line arguments to select which demo we want to run.
We will also pass in date/time, latitude/longitude,
or whatever numeric data we need for future demos.
Automated test run of the Java demos from the
unit test suite.
Adopted from https://stackoverflow.com/a/63332420
So one can run the demo with `./gradlew jar && java -jar build/libs/astronomy-demo-0.0.1.jar`
instead `./gradlew run`
