Convert build system to Gradle

[isaacbrodsky]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build #489

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-2.3%) to 94.382%

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Files with Coverage Reduction	New Missed Lines	%
src/main/java/com/uber/h3core/H3CoreV3.java	1	95.92%
src/main/java/com/uber/h3core/H3Core.java	2	94.58%
src/main/java/com/uber/h3core/H3CoreLoader.java	2	92.73%

Totals
Change from base Build #487:	-2.3%
Covered Lines:	518
Relevant Lines:	541

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💛 - Coveralls

[isaacbrodsky]

Part of #160, this is converting the build system to Gradle so that we can use the Gradle Nexus Publishing plugin (to be hooked up in a follow up PR). Everything should be set up, with the exception of some code formatting and code quality tools that will need different versions of Java / plugins.

[isaacbrodsky]

cc @nrabinowitz who Github does not prompt me to add as a reviewer :)