Add ability to have a function be templateData

[thejsj]

This is useful if you want to use something dynamically generated during the build process and want to somehow do something with that. Here's an example:

        templateData: function () {
          var envConfig = require('./client/config/json/environment.json');
          return {
            version: version,
            env: envConfig.environment,
            commitHash: envConfig.commitHash,
            commitTime: envConfig.commitTime,
            apiHost: envConfig.host
          };
        },

Would be happy to add tests/documentation/w/e else is needed if you're interested in adding this in.

[patrickkettner]

Awesome! Could you add a test for this, please?

[patrickkettner]

ping @thejsj

[thejsj]

Let me see if I can take a look at this this weekend :)

[ahc-andrew]

I would love this functionality as well