[🔥AUDIT🔥] Release v0.3.0 (#125)

🖍 _This is an audit!_ 🖍

## Summary:
We've had a few more new features in the few days since 0.2.0!  Craig
has run the webapp tests on this too.  This commit updates the
changelog, and I'll tag it with the release once it lands.

## Test plan:
crossed fingers


Author: benjaminjkraft

Auditors: csilvers, dnerdy, StevenACoffman

Required Reviewers: 

Approved By: 

Checks: ⌛ Test (1.17), ⌛ Test (1.16), ⌛ Test (1.15), ⌛ Test (1.14), ⌛ Lint, ⌛ Test (1.17), ⌛ Test (1.16), ✅ Test (1.15), ⌛ Test (1.14), ✅ Lint

Pull Request URL: https://github.com/Khan/genqlient/pull/125

docs/CHANGELOG.md

@@ -22,6 +22,16 @@ When releasing a new version:
 
 ### Breaking changes:
 
+### New features:
+
+### Bug fixes:
+
+## v0.3.0
+
+Version 0.3.0 adds several new configuration options, allowing simplification of generated types and configuration of input types, as well as marshalers for all genqlient-generated types.
+
+### Breaking changes:
+
 - Previously, `# @genqlient` directives applied to entire operations applied inconsistently to fields of input types used by those operations.  Specifically, `pointer: true`, when applied to the operation, would affect all input-field arguments, but `omitempty: true` would not.  Now, all options apply to fields of input types; this is a behavior change in the case of `omitempty`.
 
 ### New features: