Ccs811 dev

[wbvreeuwijk]

Adds CCS811 support.

Make sure all boxes are checked (add x inside the brackets) when you submit your contribution, remove this sentence before doing so.

• [x] This PR is for the dev branch rather than for the release branch.
• [x] This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• [x] I have thoroughly tested my contribution.
• [x] The code changes are reflected in the documentation at docs/*.

\<I was in need of CC811 support and found that it wasn't available, so I created this module>

[wbvreeuwijk]

My first submission to the NodeMCU