Add stivale2_struct_tag_boot_volume tag

[rdrpenguin04]

Fixes #10

Here you go! This seemed like an important feature, especially for my hobby OS, which needs to basically fetch the entire rest of itself from the disk after two seconds; not knowing where that is would make it very difficult 🙃.

This PR also pulls in the uuid crate. While this feature doesn't exactly require it to exist, it does provide an Into implementation for convenience.

[rdrpenguin04]

Force push was to disable uuid's default feature of using std

[rdrpenguin04]

Second force-push was to derive some standard traits on struct StivaleGuid.

[Andy-Python-Programmer]

I don't really feel like pulling in this crate as "required" since in the whole crate its only used once and only for a .into() implementation. This can be made into a separate feature instead which if enabled will pull in the crate and implement the into conversion method. Or on the other hand, just make the user pull in the crate by themselves which is more neat IMO since you can construct the UUID crate struct with the stivale GUID easily outside of the crate. Then you can make the fields guid and part_guid private and make a method instead which returns a reference to the stivale GUID to ensure no one mutates the fields in the structure.

[rdrpenguin04]

Alright; I'll make uuid optional. I still would like to have it, since it feels more convenient to be able to call .into() as opposed to writing out the whole constructor, but I'll bring it in as optional so people who don't need it don't get it.

[rdrpenguin04]

One more thing: it doesn't seem typical to make variables private, judging by the rest of the file; do you have a specific reason for this case?

[Andy-Python-Programmer]

Thanks @rdrpenguin04!

[rdrpenguin04]

Uh, hang on a sec; the new changes don't work