* Change OAL generator tool to runtime.
Step 1. change project structure. API links and maven pom.
* Part of metrics class generation
* Metrcis class generated.
* Set up the basic structure of new OAL engine.
* Finish metrics generation.
* Support dispatcher generation.
* Format codes.
* Generate dispatcher all methods.
* Implement disable in hardcode.
* Clear up
* Fix compile startup.
* Update license and document of new OAL engine.
* Fix rat.
* Disable class output in default
* Copy from @kezhenxu94 's test PR, https://github.com/apache/skywalking/pull/3110
* Wait for the mount command to finish
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