Prepare release

CHANGES.md

@@ -1,3 +1,22 @@
+### v0.2
+
+- Add a new `opam-0install-cudf` package (@kit-ty-kate #11).
+  This uses opam's CUDF API, allowing the solver to be used directly from within opam.
+
+- `Dir_context.std_env` now has some optional arguments, and also responds for `opam-version` (@talex5 #12).
+  You will need to add an extra `()` argument to it to upgrade.
+
+- Evaluate a package's `available` expression in `Dir_context` (@talex5 #12).
+  This isn't needed for `Switch_context` because the switch does it for us, but
+  `Dir_context` could return packages with `available: false`.
+
+- Simplify the `CONTEXT` API (@talex5 #12).
+  `candidates` now returns either `Ok opam` or `Error pkg` for each package.
+  This is clearer than using an option type and avoids the need for a separate
+  `load` function. It also makes it possible to filter packages based on the
+  content of the opam file without having to load it twice. We also no longer
+  bother loading the opam file for rejects (all we need is the name).
+
 ### v0.1
 
 Initial release.