[0.4] Code modernization

[mbabker]

Closes #51

• Adds parameter and return type declarations to method signatures where able
• Adds parameter types to class properties
• Adds visibility to all class methods and constants

[mbabker]

Assuming this and verifyExtensions will also have boolean returns when implemented. So, adding them in now to avoid the theoretical B/C break later by changing the return type from void to bool.

[mbabker]

At least on my system, 0x8000000000000000 results in a float that fails the type check for this param (int|null). Since the class also rejects negative numbers, I changed the test to cover that condition since the engine will cover the non-integer case.