Tag older releases

It would be helpful for seeing the state of the code at specific versions if each of them were tagged here in the repo instead of just released on NPM.

To tag older versions with the proper timestamp you can use a script like the following on Windows:

_tag-release.ps1_:

``` PowerShell
param([string]$version = "")
$message=(git log -1 --pretty=%B | head -1)
$env:GIT_COMMITTER_DATE=(git show --format=%aD | head -1)
git tag -a "$version" -m "$message"
```

This is a slightly modified version of [this answer](http://stackoverflow.com/a/21759466/631338) which has a version for *NIX shells.