Serialiser improvements

[magnusuMET]

I wanted to test creating/listing the index using the CLI tools, but found some functions missing. It should now be possible to create tools which can create the index, using either flexbuffers or bincode.

Also included is some other small items such as foo/mod.rs -> foo.rs and removal of fast-index as the static build of hdf5 includes this by default.

[magnusuMET]

And some clippy lints. Here is a nice message from the logs:

warning: the feature `new_uninit` has been stable since 1.82.0 and no longer requires an attribute to enable
  --> src/lib.rs:78:43
   |
78 | #![cfg_attr(feature = "unstable", feature(new_uninit))]
   |                                           ^^^^^^^^^^
   |
   = note: `#[warn(stable_features)]` on by default

[gauteh]

Great! Thanks