Add support to use BeerXML files

[drodil]

To be able to calculate for example IBU or SRM we need the incredients from the recipe. Add support for parsing BeerXML to an internal representation of the recipe that can be used by the commands.

See specification here: http://www.beerxml.com/

[mlatief]

I dread XML files, and I found there's already BeerYAML https://beeryaml.readthedocs.io/en/latest/. Also aligned with our initial thought of having parameters specified in YAML (didn't know BeerXML exists!)

[mlatief]

we can also create this a separate crate, something like (e.g. beeryaml-rust)

[drodil]

BeerXML is supported by many of the brewing tools and didn't know BeerYAML existed :D Maybe we could do a new crate for that and maybe also something to convert between these two formats ;)

[flauntingspade4]

Perhaps BeerJSON would be a good fit, as it's more readable, and not as verbose as xml?

[drodil]

@flauntingspade4 true. We'll look into that!