Improve error message for reading datapackage

[nailend]

Description

Just adds further information about which why the reading of the datapackage might not have worked. E.g which column could not be casted.

Type of change

New feature (non-breaking change which adds functionality)

Checklist:

Please tick or delete options that are not relevant.

• [x] New and adjusted code is formatted using the pre-commit hooks
• [x] New and existing unit tests pass locally with my changes
• [x] I have added new features/fixes to the CHANGELOG

[henhuy]

I like the idea, but cannot test it - do you have an example? Maybe even add a minimal test?

[nailend]

For a minimal test, I would need to add a false datapackage to examples. This might be confusing. The easiest way to check is by modifying an existing example e.g investment_multi_period/datapackage.json. Change type of field name to integer for the bus.csv and then run the `test_example_datapackage_readability``

The new error message will look like this:

E               tableschema.exceptions.CastError: 
E               Metadata structure of resource `bus` does not match data structure. Check the column names, types and their order.
E               Field "name" can't cast value "bus0" for type "integer" with format "default"

[nailend]

Can't think of a test without creating an example datapackage. Anyway, I am basically just appending the original error message to the tabular internal one. I will just merge this