fixed #220

1. Change dag graph layout from hierarchical to relationship
2. Change node style from square to round

Create CODE_OF_CONDUCT.md

Feature/164 add operation name to be a query condition in trace page.

1. add global trace id column into segment cost index.
2. just query from segment cost index when query top segment record with condition, e.g. operation name, global trace id, cost

1. add global trace id column into segment cost index.
2. just query from segment cost index when query top segment record with condition, e.g. operation name, global trace id, cost

Support new segment protocol at collector side.

sky-walking 1.0 and 2.0 are out-of-support.

2. Change the http servlet worker from local asynchronous call to local synchronous call.

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.