Convert library to no_std

[rmsyn]

Remove uses of std data structures with their equivalents in core, alloc, and hashbrown.

Also replaces the use of deprecated try!() calls with the ? operator.

Resolves #6

[rmsyn]

Ping @mbr: are you still maintaining this crate?

[orangecms]

oh hey just saw your work here @rmsyn - and the PR in part overlaps with #7 / #8

I would fork this to @platform-system-interface, but the way the crates registry works would force me to give it a new name. Org namespaces are not supported (deliberately), so I'd give it a prefix, e.g., psi_device_tree. WDYT?

[rmsyn]

That sounds good to me, just let me know what you decide on.

[orangecms]

so many projects... I have not forgotten this one, just got a bit lost with everything else. 😅

I shall rebase onto your changes :)

[orangecms]

I had originally forked it under my name, now moved here:
https://github.com/platform-system-interface/device_tree-rs