GH-1190: Added HYDRA class

[navdhaagarwal]

GitHub issue resolved: #1190

Briefly describe the changes proposed in this PR:

Added the vocabulary class for HYDRA (http://www.hydra-cg.com/spec/latest/core/)

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[barthanssens]

As mentioned in the issue 1190, code looks good (thanks !), but it would be nice if the PR could be based on develop instead of master (can simply be changed on github, so no need to create a new PR)

The reason is that we like to add new features / enhancements on develop for a new release, and only use master for bug fixes in small patch releases.

[abrokenjester]

As mentioned in the issue 1190, code looks good (thanks !), but it would be nice if the PR could be based on develop instead of master (can simply be changed on github, so no need to create a new PR)

The reason is that we like to add new features / enhancements on develop for a new release, and only use master for bug fixes in small patch releases.

Good point @barthanssens. I've changed it for this PR, so no need for any action on your part here @navdhaagarwal - but it's a good one to keep in mind: if the issue you're fixing is labeled as an enhancement, target your PR against the develop branch. Only issues labeled 'bug' should go to master. No big deal if you forget either: if you want to change this for an existing PR, click the 'edit' button to the right of the PR title, and then select a new base branch in the little dropdown.

[navdhaagarwal]

Thank you @jeenbroekstra and @barthanssens. I will keep this in mind in the future.
Please let us know if there are some modifications required.