Derive serde::Serialize for GetTransactionResultDetail et al

[casey]

We're implementing get_transaction for our dummy Bitcoin RPC server, and we need to construct and return a GetTransactionResultDetail, but GetTransactionResultDetail doesn't implement Serialize. This PR derives Serialize for GetTransactionResultDetail, as well as the types it contains.

[casey]

Just added derive(Serialize) to GetBalanceResult and GetBalanceResultEntry. Also, friendly ping if someone could take a look at this that would be awesome

[gruve-p]

@casey Can you update this PR to include ordinals#5 ?
@apoelstra Can this and #288 be merged so https://github.com/casey/ord/issues/1295 can be closed?

[nammaki]

Looks clean and simple to me 🚀

[apoelstra]

Not sure why CI didn't run on this -- but cargo +nightly fmt --check doesn't pass on this. Can you re-format?

[tcharding]

The formatting is unrelated to this PR. Fixed in #314 ... but MSRV is broken. Maybe fixed in #315

[casey]

We ran into a few other types that we needed Serialize/Deserialize implementations for. I thought that it probably isn't a good idea to add implementations piecemeal, and that all the API types should support Serialize and Deserialize if possible. I derived Serialize and Deserialize for all API types, skipping a couple where a field didn't support serialize or deserialize.

[tcharding]

ACK d85da1d

[casey]

Nice, thank you for the merge!