v1.1.0: Improve documentation, usability, tests

As seen in the sole commit of this release:

This commit introduce a lot more documentation (README, inline) in preparation for Bitblob's release.
On the functional side, it also adds an opSlice overload, make the existing opIndex overload inout,
remove the dependency on std.format, and add tests that we indeed do not allocate when using
formattedWrite.