Enhancement: Add ES and UMD builds

[ryan-roemer]

• Note: This is all @aweary 's work in Enhancement: Add ES and UMD builds #85 that is now a real project branch, with a few extra tweaks as one commit.
• Adds an ES build with ES6 modules
• Adds a UMD build using rollup

With the UMD build both prop-types and react are expected to be available on the global object before Freactal is loading. Since both of those packages have UMD builds, this should be fine.

---

The maintainers of this repo require that all pull request submitters adhere to the following:

• I have read and will comply with the contribution guidelines.
  (required)
• I have read and will comply with the code of conduct.
  (required)
• All related documentation has been updated to reflect the changes made. (required)
• My commit messages are cleaned up and ready to merge. (required)

The maintainers of this repository require you to select the semantic version type that
the changes in this pull request represent. Please select one of the following:

• major
• minor
• patch
• documentation only

[maintainerd]

maintainerd logging is enabled for this repository.

All actions related to rules and their enforcement will be logged here as a permanent record.

---

Click to view log...

• 2018-01-26T17:15:21.792Z:af63bed: The pull request was created
• 2018-01-26T17:15:38.778Z:af63bed: @ryan-roemer checked I have read and will comply with the [contribution guidelines](https://github.com/FormidableLabs/freactal/blob/master/CONTRIBUTE.md)..
• 2018-01-26T17:15:39.294Z:af63bed: @ryan-roemer checked I have read and will comply with the [code of conduct](https://github.com/FormidableLabs/freactal/blob/master/CONTRIBUTE.md)..
• 2018-01-26T17:15:40.439Z:af63bed: @ryan-roemer checked All related documentation has been updated to reflect the changes made. _(required)_.
• 2018-01-26T17:15:43.698Z:af63bed: @ryan-roemer checked My commit messages are cleaned up and ready to merge. _(required)_.
• 2018-01-26T17:16:36.387Z:af63bed: @ryan-roemer selected minor as the semantic version.

[divmain]

maintainerd is still acting up - I'm force-merging this, and will publish manually.