Raw fst .as_bytes()

[vorner]

Similar to .to_vec(), but without making copies.

Motivation

• Currently, I'm keeping a map in memory and exchange it from time to time. Later on I'd like to store it to a cache (but not at the time when I'm constructing it) and currently I have to use the to_vec and then write_all ‒ which is wasteful, because it creates a copy of the whole thing in memory.
• For some metrics I'd like to know the size of the image (not .len() ‒ that one is number of keys). Calling to_vec for that is obviously too wasteful.

If this change is OK, would it be fine to have a release with it?

Thank you

[BurntSushi]

@vorner Thanks for the PR! I'm not in principle opposed to this change. IIRC, the reason why it didn't already exist is because the &[u8] tends to be a memory map, or at the very least, could be a memory map. In that circumstance, getting access to the raw slice without needing to type unsafe would be bad. With that said, in the last release, I made it so constructing an FST from a memory map required typing unsafe. See here and here and here. There is even a safe method called as_bytes on the MmapReadOnly type. So to that end, I think the lack of this method is just an oversight and this should be OK!

[BurntSushi]

This PR is now on crates.io in fst 0.3.3.

[vorner]

Thank you :-)

What I was thinking ‒ accessing the slice should not be more dangerous than doing .search or something like that on the fst anyway.