Support pre-population of tools form with url parameters

[fbuchinger]

It would be great if the fields of the "online tools" form could be pre-populated via URL parameters:

https://emn178.github.io/online-tools/sha256.html?input=to_be_hashed_string&type=text&hash=sha256

That would allow for a quick verification of shorter hashes.

[emn178]

added this feature