Updates for Phoenix 1.7

[jfreeze]

[WillRochaThomas]

Thanks for creating this PR @jfreeze, I've had to hurriedly copy your changes into our fork as we needed them too https://github.com/getdizzie/scrivener_html. I know a few people have started forks, but nothing seems to have turned into proper hex published package – maybe we need to turn our fork into something proper that others can contribute to & use more easily.