For home's changesapp to be able to navigate to historyapp directly 
via SPA.

For home's dark mode support.

It will be used for setting the onclick property for anchor elements.
This is needed for https://github.com/shurcooL/home/issues/40.

Make the BSD 3-Clause license easier to see by adding a LICENSE file
to the repository. Use the same format as https://golang.org/LICENSE.

Follows https://github.com/shurcooL/octicon/commit/c42b0e3b24d96976ecac81ef691662777b39ef64.

Follows https://dmitri.shuralyov.com/state/...$commit/28bcc343414c6adcd7b6911f9d0ef1ad6fbf30ae.