Include perf improvements in release notes

- Include perf improvements in release notes 
  (per https://meta.discourse.org/t/include-performance-improvements-in-release-notes/21895)

- Add ability to specify 'from' and 'to' tags in rake task:

```
# generate release notes for changes between v1.1.0 and v1.1.0
$ rake release_note:generate[v1.0.0,v1.1.0]

# generate release notes for all changes since v1.1.0
$ rake release_note:generate[v1.0.0]

# generate release notes for all changes since last tag
$ rake release_note:generate
```