Generate the correct git changelog for the 0.5.0 release.

Tweak the text of release/$VERSION/index.html.

doc/release-index.md

@@ -52,10 +52,10 @@ Oil Version 0.5.0
- [osh2oil Tests](test/osh2oil.wwz/log.txt).  Test the conversion of OSH to
  Oil.

#### OPy Tests
### OPy Tests

The OPy compiler is used to compile Oil, but it isn't technically part of the
release.  Here is some rough evidence that it works.
The OPy compiler is used to compile Oil to bytecode, but isn't itself part of
the release.

- [build-oil-repo](test/opy.wwz/build-oil-repo.txt)
- [test-gold](test/opy.wwz/test-gold.txt)

scripts/release.sh

@@ -424,9 +424,13 @@ git-changelog-0.5.alpha3() {
    > _release/VERSION/changelog.html
}

# Hm if you're not releasing on the same machine as the previous release, the
# branch needs origin/ on the front?  Is this the best way to do it?
# NOTE: 'git branch -a' shows all branches.

git-changelog-0.5.0() {
  # NOTE: release/0.5 branch should be sync'd up with master squashes.
  _git-changelog release/0.5.0 release/0.5.alpha3 \
  _git-changelog origin/release/0.5.alpha3 release/0.5.0 \
    > _release/VERSION/changelog.html
}