Support for MetaRx / Widok

[mkotsbak]

Would be nice if support for https://github.com/MetaStack-pl/MetaRx was added. As it probably adds a dependency, it should probably be placed in a separate module.

[travisbrown]

@mkotsbak I'm not very familiar with MetaRx—what do you imagine this support looking like?

[zarthross]

@mkotsbak this would be the responsibility of MetaRx or a 3rd party library to implement, not Circe.

[mkotsbak]

Yes, it probably should be done inside MetaRx, as done for uPickle: tindzk/MetaRx@d5beeb6

I opened issue tindzk/MetaRx#58 for this.