Layer validator

[isaisabel]

Both #1 and #2 should validate input and output layers to make sure they match the schema. The validation function should be both generalized and flexible to multiple use cases.

• An optional flag should be provided for allowing layers to include additional fields in the schema (non-strict checking). If the flag is not present the script will report a break from the schema as soon as an unexpected field is present.
• The script should be able to return multiple kinds of reports.
  • whether or not the layer is valid (boolean)
  • list of ways the layer does not conform to the schema
  • human readable report on how the layer does not match the schema, for printing to the console

[isaisabel]

Now released on the master branch