Add fwdinghistory method

[matthewbotti]

Hello, first, I love the library which made it much easier for me to work with the grpc lnd client.

That said, the one feature I needed to build my app uses the 'fwdinghistory' argument from lncli, would it be possible to add that as a method in your library - I tried looking for it, but doesn't seem to exist, if it does, please let me know.

Thank you for your time and contribution to the LN ecosystem.

[adrienemery]

Hi, I'm glad it's been useful for you.

As I don't have a ton of time to put towards this project right now are you able to submit a PR for this? I can point you in the right direction if you are interested.

If not I can add it but it might take a bit longer.