Display a correctly formatted value when reporting invalid values

[jpmckinney]

For example:

• Showing what a valid date looks like when reporting an invalid date
• Displaying the value surrounded by quotes, when reporting a non-string

Split from document linked in #101

[jpmckinney]

lib-cove-ocds has "Incorrect date format. Dates should use the form YYYY-MM-DDT00:00:00Z. Learn more about dates in OCDS."

lib-cove-web has:

• {}<code>{}</code> is not a string. Check that the value {} has quotes at the start and end. Escape any quotes in the value with <code>\</code>
• {}<code>{}</code> is not a integer. Check that the value {} doesn’t contain decimal points or any characters other than 0-9. Integer values should not be in quotes.
• {}<code>{}</code> is not a number. Check that the value {} doesn’t contain any characters other than 0-9 and dot (<code>.</code>). Number values should not be in quotes.

So, this issue is already done.