Return error instead of panics on invalid ASN.1

[Flakebi]

Hi,
I use this library to find out if something is ASN.1 or not, unfortunately it often panics on invalid input.
To find all panics I added a cargo-fuzz project and fixed all the panics it found.
With the final version, the fuzzer did not find any panic for half an hour.

Unfortunately this pr currently includes a breaking change because it adds error variants. So I’m not sure if you want to implement this someway else, e.g. return some of the existing errors instead.

Edit: I found this commit which also adds a + Error bound to the error types.

[acw]

This is awesome, and I'm always happy to add more (and more helpful) error variants. Let me check a couple things and then I'll merge it.

[Flakebi]

Thanks!

One thing I forgot to mention: The GeneralizedTime parser previously inserted the dot at position 15, 14 should be the right position :)

[acw]

Yes, I saw that and that was one of the things I wanted to look at (and maybe write a test case for). :)

[acw]

This version has been pushed as 0.4.0.