1. Remove the “apm-trace” module, isolate the trace structure between agent and collector for considering performance.
2. Change the head name.
3. Provide potienal mechanism for ignore trace with certain suffix.

* master:
  add message/stack length check when skywalking convert throwable stack to string.
  Delete _config.yml

# Conflicts:
#	apm-commons/apm-trace/src/main/java/org/skywalking/apm/trace/Span.java

Fix OutofMemory of Span.ThrowableTransformer.convert2String

Official website has already been provided. Don't need this file.

Add @xcaspar in the contributors list.

Fix witness class fail, because of different class loaders.

Fix the wrong key of poolMap

* 'master' of https://github.com/wu-sheng/sky-walking:
  update docker image version
  Update the http port of collector server
  Provide new data protocol for segment messages.
  chore(collector): add a check for process id in startup script

chore(collector): add a check for process id in startup script

update docker image version

Update the http port of collector server

Provide new data protocol for segment messages.

This reverts commit 323468f0.

This reverts commit 5b853ec3.

This reverts commit 19f2a561.

This reverts commit 323468f0.

This reverts commit 04041ebd.