feat: improved documentation site and release process

[maoo]

Dear ContextData team,

as discussed in the last FDC3 PMC, I'm sending a Pull Request to enable generation of documentation within the ContextData repository, as done for the API Working Group

The current result can be demoed on http://fdc3-context-data.finos.org ; please note that this deployment is based on my fork, nothing have been altered in the github.com/FDC3/ContextData repository.

Please note that:

• The code points to pending Pull Requests, such as FDC3/FDC3#1 , which defines the common HTML/CSS site layout and main navigation
• After merging, some changes must be applied to fork-specific code pointers (see TODOs in .travis.yml)
• After merging, some changes must be applied to Travis CI settings, in order to use proper deployment keys

More info on the release and documentation publishing can be found on https://finosfoundation.atlassian.net/wiki/spaces/FDX/pages/75530469/Project+documentation

Thanks,
mao