WIP: Re #5 - Parameter schema + refactor for Unit and Value schemas

[marshallmcdonnell]

Work includes:

• Adds the parameter schema
• Refactors the unit and value schemas
  • more DRY (Don't Repeat Yourself) using the definitions section
• Switches to testing with pytest
  • Testing required using "linked" or "chained" schemas (i.e. context -> unit -> value -> parameter) that arose with creating the parameter schema. Needed scripting with jsonschema package, not just CLI
  • Includes testing valid JSON-LD in examples/sections as well as invalidating "bad" schema found in the tests themselves such as bad values and additional properties that shouldn't be there.

Blocked by: MR #7 needs to be merged first so we can rebase off that work

[marshallmcdonnell]

@stuchalk So this one should be ready except needs MR #7 approved and merged first (will rebase this feature off those changes going in)

This one re-writes the Unit and Value schema based on the need that arose with Parameter schema setup (and only realizing that by creating the tests :grin:)

Pretty happy though, it is checking for valid schema in the examples/sections directory + validating "bad" schema too in the tests.