! change package of agent related classes, prepare for open agent for extension by agent/transformlet developer

- split common_build from ttl_build
- use MVN function instead of MVN_CMD array

- no lib user runtime cost, still runtime 0-dependency
  not runtime/compile Transitive dependence
- more IDE friendly
  ensure to be able to jump to annotation class(edu.umd.cs.findbugs.annotations.NonNull, etc)
  when user browse source code in IDE

use project.build.finalName instead of ${project.artifactId}-${project.version}

more info see:

- http://maven.apache.org/pom.html#BaseBuild_Element
- https://stackoverflow.com/questions/20859734/what-is-the-value-of-project-build-finalname
- https://stackoverflow.com/questions/4238944/controlling-maven-final-name-of-jar-artifact

- add benefits and advantages about TransmittableThreadLocal
- add faq
- add 3rd party introduction articles

- fix shellcheck warning
- Quote strings to prevent word splitting
- rename functions:
    - runCmd -> logAndRun
    - private internal function name with prefix __
- fix typo
- rename source guard within uuid

more info see:
https://github.com/codecov/example-java-maven/blob/master/.travis.yml

Merge pull request #230 #233

Bump kotlin.version from 1.4.21 to 1.4.21-2

Updates `kotlin-stdlib` from 1.4.21 to 1.4.21-2
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog-1.3.X.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

Updates `kotlin-maven-plugin` from 1.4.21 to 1.4.21-2

Bump spotbugs-maven-plugin from 4.1.4 to 4.2.0

Bumps [spotbugs-maven-plugin](https://github.com/spotbugs/spotbugs-maven-plugin) from 4.1.4 to 4.2.0.
- [Release notes](https://github.com/spotbugs/spotbugs-maven-plugin/releases)
- [Commits](https://github.com/spotbugs/spotbugs-maven-plugin/compare/spotbugs-maven-plugin-4.1.4...spotbugs-maven-plugin-4.2.0)

- link release action list
- Bootstrap ClassPath problem

Merge pull request #227

Bump kotlin.version from 1.4.20 to 1.4.21