create unit tests for various number formats

[hendrixjoseph]

For issue #657 Unit tests should check various number formats

This adds tests for various number formats (namely: decimal with and without a decimal point, exponent with both capital and lowercase E, both in the positive and negative) for the various get* and opt* number methods of JSONObject.

It does NOT add hex, floating point hex, or octal, as these are not supported JSON features (see https://stackoverflow.com/a/52671839/6323312). JSONObject also does not support hex, floating point hex, or octal.

I can add these additional number format tests if wanted, though.

[stleary]

What problem does this code solve?
Adds some missing unit tests.

Risks
Low

Changes to the API?
N/A

Will this require a new release?
No

Should the documentation be updated?
No

Does it break the unit tests?
No

Was any code refactored in this commit?
N/A

Review status
APPROVED

Starting 3 day comment window