Add the TXO's value to the response from get_mempool since we have it

[doc-hex]

The response from API call blockchain.address.get_mempool lists the transaction hashes but did not include the TXO amount, even though it's right there already (as 'delta').

This is a simple one-line change, which adds the additional data to the response, using the field name value to align with other responses.

Unfortunately, I don't have the means to test this change, and a number of API responses will be affected because they call get_unconfirmed_history() indirectly. Hopefully clients are going to ignore new JSON fields.

[lclc]

get_mempool is not used by the Electrum-Client (or any other client I'm aware of) afaik, so shouldn't affect many users

For what do you use it?

[doc-hex]

I want to show a detailed balance of an address. For unconfirmed amounts it was not possible to show the breakdown of which transactions contribute how much to the unconfirmed balance.

This addition will also show up in blockchain.address.get_history for unconfirmed amounts.

[doc-hex]

Anniversary bump.