Incomplete ReadMe

[wknowleskellett]

Maybe this is opinionated, but until a 1.0 release, I think the readme needs to address why that hasn't been reached yet, and some notion of what hardened features people can expect to persist across pre-1.0 releases, since semver alone provides no guarantees prior to the first full release.

Cheers! Looks cool, would love to invest more attention in the library if it quantified its longevity. I was recommended to use it by someone who thinks highly of it.

[mcmah309]

Macros are a little funky since a "bug" can break compilation. While with regular code this does not happen. That is why I would like error_set to be "feature complete" before shipping 1.0.0. That said error_set is fairly complete at the moment. I don't foresee any intentional breaking changes.