Add CI release workflow, CHANGELOG.md, issue templates

- .github/workflows/release.yml: on tag push, build exe via ps2exe,
  package portable zip, attach SHA-256, create GitHub Release.
- CHANGELOG.md: Keep a Changelog format, semver.
- .github/ISSUE_TEMPLATE/: bug_report.yml + feature_request.yml + config.yml
  routing security reports to private advisories.

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -0,0 +1,23 @@
+name: Feature request
+description: Suggest a new feature or an improvement
+labels: ["enhancement"]
+body:
+  - type: textarea
+    id: motivation
+    attributes:
+      label: What's the use case?
+      description: What are you trying to do, and why is the current behavior not enough?
+    validations:
+      required: true
+
+  - type: textarea
+    id: proposal
+    attributes:
+      label: Proposed solution
+    validations:
+      required: true
+
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives considered