Basically everything that has a direct replacement or no uses left.
Notable omissions:
- std.ArrayHashMap: Too much fallout, needs a separate cleanup.
- std.debug.runtime_safety: Too much fallout.
- std.heap.GeneralPurposeAllocator: Lots of references to it remain, not
a simple find and replace as "debug allocator" is not equivalent to
"general purpose allocator".
- std.io.Reader: Is being reworked at the moment.
- std.unicode.utf8Decode(): No replacement, needs a new API first.
- Manifest backwards compat options: Removal would break test data used
by TestFetchBuilder.
- panic handler needs to be a namespace: Many tests still rely on it
being a function, needs a separate cleanup.
* `doc/langref` formatting
* upgrade `.{ .path = "..." }` to `b.path("...")`
* avoid using arguments named `self`
* make `Build.Step.Id` usage more consistent
* add `Build.pathResolve`
* use `pathJoin` and `pathResolve` everywhere
* make sure `Build.LazyPath.getPath2` returns an absolute path
