Switch back to upstream github.com/kidoman/embd with fixes

[SpComb]

Fixes #29

Switch back to the upstream github.com/kidoman/embd from our own fork, it now has the relevant fixes merged:

• https://github.com/kidoman/embd/commit/c1886eb5bf22bf655793ce7c50491175de95923f
• https://github.com/kidoman/embd/pull/68/commits/091d6f558821db718702f1dd9636637d2c429d6f
• https://github.com/kidoman/embd/commit/1e99d1ac2d1ebab3faf03fcf7d6fcf78ea9ef824