triple release: ostree v2021.2, new crates.io/crates/ostree{, -sys,-ext}

["Colin Walters" <walters verbum org>]

This is the first "triple release" of the core libostree: 
https://github.com/ostreedev/ostree/releases/tag/v2021.2

Plus releases of the Rust bindings now merged into our organization:
https://crates.io/crates/ostree/0.11.0
https://crates.io/crates/ostree-sys/0.7.3

And finally the first release of the new `ostree-ext` Rust crate (library):

https://crates.io/crates/ostree-ext/0.1.0

The high level plan here is that we keep the existing C code as is but start adding new high level features 
in Rust.  I'd like to encourage project consumers to use Rust.  It's very early days for `ostree-ext` and a 
lot may change.  (See more on that below)

There's also likely going to be an `ostree-ext-cli` crate soon (it's in git), but it's just a really thin 
wrapper around the library.  I think we need to do some discussion around the future of the `/usr/bin/ostree` 
CLI.  


### ostree v2021.2


Release 2021.2

This release mainly adds new APIs for file writing, which we will
use in the new ostree-rs-ext project to improve imports from tarballs.
The other feature is that rofiles-fuse now handles xattrs (but - rofiles-fuse
should be considered deprecated, see https://github.com/ostreedev/ostree/issues/2281 ).
There's also some more introspection API tweaks, and some testing improvements.

Thanks to all contributors!

```
Benjamin Gilbert (1):
      docs: fix "Edit this page on GitHub" links

Colin Walters (25):
      configure: post-release version bump
      .lgtm.yml: Add package deps
      installdeps: Drop PyYAML
      tests/pull-test: Use mv -f in a few cases
      cci: Update for buildroot changes
      repo: Fix load_variant_if_exists to return a nullable value
      repo: Ensure load_variant_if_exists sets NULL value
      build-sys: Include all mkinitcpio bits
      manual-tests: Fix unused variables
      core: Fix lgtm.com warning about always true `if (bits > 0)`
      tests: Drop openat override
      tests/inst: Update ostree crate
      tests/inst: Update rpm-ostree client
      tests/inst: Update tokio, hyper and nix
      build-sys: Remove --enable-experimental-api
      core: Drop unused error handling from object stream helper
      tests: Silence a gcc warning
      repo: Add ostree_repo_write_regfile_inline
      travis: Bump Ubuntu versions
      repo: Add ostree_repo_write_symlink
      repo: Add ostree_repo_write_regfile
      tests: More tests for inline writing
      repo: Ensure we set the size for regfile inline
      Release 2021.2
      configure: post-release version bump

Dan Nicholson (6):
      Remove apidoc .gitignore from version control
      Ensure consistent apidoc .gitignore
      travis: Don't ask any debconf questions when installing packages
      travis: Drop i386 Ubuntu target
      travis: Correct ci_suite settings for buster
      travis: Add back a 32 bit i386 build

Felix Krull (1):
      lib: fix some version tags

Stefan Berger (1):
      rofiles-fuse: Enable support for setting and getting xattrs
```

# ostree-ext v0.1.0:

This is the first release; the headlining feature is a new lossless tar import/export model and PoC work on 
OCI/Docker import/export on top of that.  There's a lot still to do here; in particular 
https://github.com/ostreedev/ostree-rs-ext/issues/2 would need to be fixed to take this more seriously.  But 
it's suitable for experimentation.

There are also other convenience methods in ostree-rs, such as a new diff API, etc.