📝 Add changelog (#51)

CHANGELOG.md

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+<!--
+Guiding Principles:
+
+Changelogs are for humans, not machines.
+There should be an entry for every single version.
+The same types of changes should be grouped.
+Versions and sections should be linkable.
+The latest version comes first.
+The release date of each version is displayed.
+Mention whether you follow Semantic Versioning.
+
+Usage:
+
+Change log entries are to be added to the Unreleased section under the
+appropriate stanza (see below). Each entry should ideally include a tag and
+the Github issue reference in the following format:
+
+* (<tag>) \#<issue-number> message
+
+The issue numbers will later be link-ified during the release process so you do
+not have to worry about including a link manually, but you can if you wish.
+
+Types of changes (Stanzas):
+
+"Features" for new features.
+"Improvements" for changes in existing functionality.
+"Deprecated" for soon-to-be removed features.
+"Bug Fixes" for any bug fixes.
+"API Breaking" for breaking exported APIs used by developers building on SDK.
+Ref: https://keepachangelog.com/en/1.0.0/
+-->
+
+# Changelog
+
+## [v0.2.0](https://github.com/skip-mev/skip-api-contracts/releases/tag/v0.2.0) - 2023-08-03
+
+[Tracking](https://github.com/skip-mev/skip-api-contracts/issues/28)
+
+### Notable Features
+- [#21](https://github.com/skip-mev/skip-api-contracts/issues/21) Support swap exact out for the user, refunding unused input token back to a refund address on the swap chain.
+
+### Notable Improvements
+- [#31](https://github.com/skip-mev/skip-api-contracts/pull/31) Derive user swap coin in from remaining coin received only
+- [#32](https://github.com/skip-mev/skip-api-contracts/pull/32) Upgrade cosmwasm_std to 1.3
+- [#36](https://github.com/skip-mev/skip-api-contracts/pull/36) Derive Fee Swap Coin Out From IBC Fees Provided
+- [#42](https://github.com/skip-mev/skip-api-contracts/pull/42) Upgrade Rustc to 1.71.0, Workspace to 2.0, and CosmWasm Optimizer to 0.14.0
+
+### Notable Other Changes
+- [#38](https://github.com/skip-mev/skip-api-contracts/pull/38) Affiliate fee BPS based off of `min_coin` instead of the coin received from the swap itself.
+- [#19](https://github.com/skip-mev/skip-api-contracts/pull/19) IBC adapter contracts refund the user based off of querying the contract balance rather than relying on stored variables.
+- [#33](https://github.com/skip-mev/skip-api-contracts/pull/33) Replace custom impl of Coins with cw_std Coins 
+
+## [v0.1.0](https://github.com/skip-mev/skip-api-contracts/releases/tag/v0.1.0) - 2023-07-18
+
+Let There Be Skip API Contracts!
+
+### Features
+- Supports swap exact in for the user.
+- Supports three post-swap actions:
+    - Bank Send
+    - IBC Transfer
+    - Contract Call
+- Supports a fee swap if the post swap action is an IBC transfer and requires IBC fees.
+- Supports affiliate fee payments.
+
+### Network / DEX Support
+- Osmosis: Poolmanager, Neutron: Astroport