Minor changes to specification v0.10.1-develop

[CasperWA]

There are currently minor changes to the specification of v0.10.1-develop.
More may come and should be added below.

Schema / Models

• Change from homepage_url to homepage (Change homepage_url -> homepage in providers.json and add it to examples OPTIMADE#238)
  • Fixed by Added homepage attribute to LinksResource #127
• A BaseResource for relationships may contain a meta field alongside id and type, with the field description (Correct the description of where relationships should go OPTIMADE#232)
  • Fixed by Add meta.description to BaseRelationshipResource #131
• Allow only float or None values for the lattice_vector content (within the list of lists), (Clarify use of null in lattice_vectors OPTIMADE#231)
  • Fixed by Updated structure models and validators #126
• Add homepage_url field to LinksResourceAttributes (Add 'homepage_url' to providers.json OPTIMADE#228)
  • Fixed by Added homepage attribute to LinksResource #127
• New REQUIRED levels of response properties (Update models with new levels of REQUIRED response properties #114)
  • Note: This affects querying as well as the schema requirements.
  • Fixed by New REQUIRED level properties #153

Grammar

• Update definition of LengthComparison (Refining the grammar of the LengthComparison OPTIMADE#221)
  • Fixed by Introduce grammar v0.10.1 #112
• No constant <operator> constant comparisons allowed for strings (Forbid constant <op> constant comparisons for strings OPTIMADE#229)
  • Fixed by Introduce grammar v0.10.1 #112

Miscellaneous

• OPTIONAL: Implement a landing page for requests to the base URL (Explain what to return for requests to the base url OPTIMADE#227)
• Update the base URL from where the server is served (disable serving API under /v0.10 and /v0.10.0 by default? #122)
  • Fixed by Update base URLs #155

[ml-evs]

Any of these in progress atm? I'm happy to take the model updates (excl #114) and have a go at a landing page when I get a chance later.

[ml-evs]

Just knocked off a few of these in #126, but I'm confused about this homepage stuff.

We already have the homepage attribute in our Provider model, but not in Links (which has its own subtype called Provider)... simply adding it to the model and updating the index_links.json and test_links.json causes a lot of errors for me, which I don't have time to look at right now. I'll open the PR and leave it hanging.

[CasperWA]

Closing this and adding an issue specifically for the remaining OPTIONAL task.