Add hex key support

[virusvfv]

if key begins from 0x... then key will be interpreted as hex key. If there is an error with hex decoding (ex: 0xblabla or 0x111) key will be empty.

[ozzi-]

Hi @virusvfv

Thanks for the PR! I made some changes:

• the edge case, that the key starts with 0x but isn't actually hex, is now supported instead of an empty key & error being logged
• refactoring

:)