Adds endpoint to emulate inbound funds

[mdesousa]

Add the following endpoint to emulate inbound funds:

• POST /v2/demo/funding/create

This is very useful for testing purposes and allows developers to take advantage of the sdk features used for other endpoints.

[anthonygood]

This would save us some work implementing this missing functionality outside of the SDK.

[mdesousa]

hello @jonathancouchman @gergelykovacs , wondering if you had a chance to review this?
by the way, i looked through those static code analysis warnings but they seem inconsistent with the existing code? for example, i see warnings about strings requiring double quotes... but i see the existing code uses single quotes.
it would be very helpful to get this merged in the library, thanks.