Improve error messages

[roll]

Overview

[from @Mikanebu]

Also, when I got an error message, it was not clear:

• Wrong type for header: Coordinates and value: -14.27667
  Suggestion: Coordinates field cannot accept value -14.27667. Geopoint type should be in the pattern "lon, lat".
• Row X is completely blank { "error-count": 1, "headers": [ "Country Name", "Country Code", "Year", "Value" ], "time": 0.406, "row-count": 1000, "source": "gdp/data/gdp.csv", "valid": false }
  This error message has unnecassary information and not clear.
  Suggestion: Row X is completely blank. According to the spec it cannot be accept empty rows. Path to source
• Row 7 is duplicated to row(s) 6
  Same here
• When schema type is not type of *array*.
  Too much information and not clear.
  Suggestion: Failed validating 'type' in schema['properties']['sources']. Sources property type must be type of array.
• AttributeError: 'list' object has no attribute 'split'
  Wrong geotype error which is not clear.
  Probably it is kind of bug

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[from @roll]

I agree on some but others are clearly from goodtables not from tableschema-js.

[Stephen-Gates]

Just wondering if the errors messages presented are using https://github.com/frictionlessdata/data-quality-spec/blob/master/spec.json?

The messages above are similar to but not the same as the spec:

• Row X is completely blank is L77 but the description doesn't seem to match
• Row 7 is duplicate to row(s) 6 is L85 but the description doesn't seem to match

These don't match the spec at all:

• Wrong type for header: Coordinates and value: -14.27667
• When schema type is not type of *array*
• AttributeError: 'list' object has no attribute 'split'

The Data Quality Spec seems to have a good set of messages and I imagine foreign key errors messages will be added soon. Should this library use the Data Quality Spec?

[roll]

@Stephen-Gates
I think it's a really good idea. I'm merging all error-related suggestions to #77 to handle it for v1

[roll]

MERGED
#77