Add preversion, version, and postversion scripts

[dan-f]

npm has some nifty script hooks for automating our versioning flow. See the documentation from npm help version:

       If  preversion,  version,  or  postversion are in the scripts property of the package.json,
       they will be executed as part of running npm version.

       The exact order of execution is as follows:

       1. Check to make sure the git working directory is  clean  before  we  get  started.   Your
          scripts  may  add  files  to  the  commit  in future steps.  This step is skipped if the
          --force flag is set.

       2. Run the preversion script. These scripts have access to the old version in package.json.
          A  typical  use  would  be running your full test suite before deploying.  Any files you
          want added to the commit should be explicitly added using git add.

       3. Bump version in package.json as requested (patch, minor, major, etc).

       4. Run the version script. These scripts have access to the new version in package.json (so
          they  can  incorporate  it  into  file  headers in generated files for example).  Again,
          scripts should explicitly add generated files to the commit using git add.

       5. Commit and tag.

       6. Run the postversion script. Use it to clean up the file system or automatically push the
          commit and/or tag.

       Take the following example:

         "scripts": {
           "preversion": "npm test",
           "version": "npm run build && git add -A dist",
           "postversion": "git push && git push --tags && rm -rf build/temp"
         }

       This  runs all your tests, and proceeds only if they pass. Then runs your build script, and
       adds everything in the dist directory to the commit. After the commit, it  pushes  the  new
       commit and tag up to the server, and deletes the build/temp directory.

Since we're already handling building during publish, I think we should add something like assuming we want to publish every time we bump the version (maybe we don't?):

"preversion": "npm test",
"postversion": "git push --follow-tags && npm publish"

We can also automate releasing to GH Pages as part of this.

[dmitrizagidulin]

Implemented, closing.