added services v2.1 api page

renamed writing-service -> api-v2.0

added a redirect page for the missing page

[#61758830]

Conflicts:
	source/docs/running/architecture/services/writing-service.html.md.erb
Service Broker API 2.1 doc updates. [#61758830]
added services v2.1 api page

renamed writing-service -> api-v2.0

added a redirect page for the missing page

[#61758830]

Conflicts:
	source/docs/running/architecture/services/writing-service.html.md.erb
Service Broker API 2.1 doc updates. [#61758830]
Merge branch 'api21' of github.com:cloudfoundry/cf-docs into api21
Merge pull request #240 from cloudfoundry/api21

Api 2.1