CASSJAVA-109: Manual and API References after donation

[SiyaoIsHiding]

Using the tool mkdocs to build our doc.

Changes mainly consist of the following parts:

1. Adding mkdocs.yaml for configuration, and removing the obsoletedocs.yaml
2. Symlinks. It's a workaround of the bug that mkdocs does not recognize relevant paths that start with ../
3. Fixing Javadoc errors in DefaultDriverOption and CqlVector
4. Plugin goals' configuration in pom.xml to aggregate javadocs from multiple modules
5. Build script build-doc.sh to generate & aggregate javadoc, move them to under manual/ path, build doc with mkdocs, and then remove the javadoc under manual/