hashmap: a libgit2-idiomatic khash by ethomson · Pull Request #6897 · libgit2/libgit2

Introduce `git_hashmap` and `git_hashset` functionality that is a port
of `khash.h` to be more idiomatically libgit2. This gives us many of the
benefits of khash that we had abstracted away:

1. Typesafety on the values, since we define the structs and functions
2. Ability to create hashes on the stack
3. Ability to new up hashmaps (or sets) without the libgit2 abstraction
   wrappers that we had been adding

This uses the macros to define hashes (either the structure, or the
functions, or both) which is very much in the spirit of khash, but
the results are much more idiomatically libgit2.