Add abistr support

[MaulingMonkey]

Against readme goals:

• No dependencies (minimal build times)

But it could be hidden behind a non-default feature.

Would allow me to get rid of O(N) nonsense:

minidl/src/lib.rs

Line 117 in 1cd5c29

assert!(!name[..n-1].contains('\0'), "symbol name mustn't contain '\0's, except to terminate the string");