* Protoc plugin fails when build

* add doc for TraceCrossThread

Add an incubating feature in SkyWalking documents.

* Collector 5.0.0-alpha version upgrade FAQ.

* Update Upgrade.md

Reformat document and adjust some English.

* Add link.

* Provide document for TLS

* Provide direct uplink doc.

* Add namespace document.

* Provide token auth doc.

* Provide setting override document.

* Fix two typo.

* Fix more typos.

* Update docs for alpha release

* Delete a comma.

* Update How-to-build.md

* Add data-set licenses file

* Rename LICENSES-data-set to LICENSE-data-set

* Update LICENSE

* Remove fastclick from LICENSE

* Make the git submodule command to be a maven profile plugin. Let this command not execute by default install command.

* [maven-release-plugin] prepare release apm-5.0.0-alpha

* [maven-release-plugin] prepare for next development iteration

* Product name is not correct

* Add more documents for release.

* Change profile id.

* Add CHANGES file in distribution file.

* Revert "[maven-release-plugin] prepare for next development iteration"

This reverts commit ac815019.

* Revert "[maven-release-plugin] prepare release apm-5.0.0-alpha"

This reverts commit 095597c9.

* Add rat plugin to check dependency license and add license head into missing files.

* Fix docs.

* Exclude web ui config file.

* Next release guide.

* UI update.

* Update docs.

* Build source shell.

* Proposal our ROADMAP.

* Update ROADMAP.md

* Update ROADMAP.md

* Update ROADMAP.md

* Update ROADMAP.md

* Update ROADMAP.md

Remove already supported from roadmap.

* Update ROADMAP.md

Add UI roadmap

* Update ROADMAP.md

* Update ROADMAP.md

* Update ROADMAP.md

* Update ROADMAP.md