Update error messages to be more plain-English like, and give all errors a type to make customising error messages easy and reliable.
Error types in README
Less passive aggressive error for min/max failures
Tests for error types
Merge pull request #1 from gocardless/error_types

Update error messages to be more plain-English like, and add error types
Title levels in the README
Merge pull request #2 from gocardless/error_types

Title levels in the README
Better error message on non-schema schema
Move detailed errors docs to separate file
Link to docs in readme
Merge pull request #15 from gocardless/master

Update error messages, add error types