Revert "Remove submodules"

This reverts commit a3b4e7cbda5eaee1b5a1458ad4544eb151d46be3.
Revert "Fix merge error."

This reverts commit 160095e00a1eb926363c8c24e5c51a3049a7d99b.
Revert "Create gh-pages branch via GitHub"

This reverts commit ddc3c93f6d96460174c0291c9ec0e38ee5128a54.
Revert "Revert "Create gh-pages branch via GitHub""

This reverts commit 256a1bb300ef0ca20254a2da12fc8484d3fa3323.