change nested value structure; add toString to all values

[jraymakers]

• Change structure of value several value objects, including ARRAY and LIST to be JS arrays instead of vectors, and STRUCT to be a JS object.
• Add toString implementations to all values, including date, time, timestamp(s), interval, decimal, blob, bit, and uuid.
• Fix a bug in reading bools from a bit value.
• Add Min and Max value constants to primitive type classes and non-primitive value classes.
• Remove generic type argument from array and list vectors.
• Use the above to simplify the API unit tests.
• Add unit tests for toString implementations.