Add CHANGELOG and CODEOWNERS (#493)

CHANGELOG.md

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+# Changelog
+
+## Conway spec
+
+### WIP
+
+- Rename `ccTermLimit` to `ccMaxTermLength`
+- Add `Vote` and `Propose` script purposes
+- Well-formed parameter updates can't be empty
+- Add reward withdrawal restriction
+- Add `pvCanFollow` check to `GOV` STS
+- Fix treasury withdrawals
+- Add `policy` field to `GovProposal`
+- Add `Voter` type and use it for `ScriptPurpose`
+- Add `minFeeRefScriptCoinsPerByte` protocol parameter
+- Add security-relevant parameters
+- Require reference inputs to be disjoint from regular inputs
+- Fix CC expiration not being considered for `ccMinSize` check
+- Replace `allEnactable` with `hasParent` in `GOV`
+- Add `curTreasury` field to transactions
+- Compute the voting stake distribution
+
+### V0.9
+
+- Add proposal deposits
+- Add proposal policy (which would become the guardrails script)
+- Cold keys are now cold credentials
+- Fix: governance actions were removed immediately, now delayed by one epoch
+- Increment DRep activity in epochs where there was no GA to vote on
+- Only allow votes for GAs that actually apply
+- CC rejects every proposal when below `minCCSize`
+- Fix that `RATIFY` wasn't total
+- Properly implement treasury withdrawals
+- Remove unused hot credentials at the epoch boundary
+- Implement proper vote counting for SPOs
+- Fix some protocol parameter names
+- Check that `NewCommittee` actions are sensible when they are proposed
+- Fix: treasury withdrawals were included in the wrong map
+
+### V0.8
+
+First draft

CODEOWNERS

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+. @whatisRT