Enable caching on non-https pages

[klesun]

As I found out today, the caching does not work on non-https pages because crypto.subtle is only available in secure contexts, and I use it for sha256 hash of compiled code to detect changes.

Some collision-resistant version of inlined crc function would do, though need some googling. In the worst case I don't find any simple solutions, I have a very stupid idea - to split hashed text into 8 chunks and use crc32 on each of them, then concat digests.