Handle string values in the gdb registers output

[IddoPuff]

previously causing crash, now ignoring specific register

Fixes #36

[anfedotoff]

Can you, please:

1. Fix test_stacktrace_structs, it's seems to me, that offset of the compiled binary has changed. You can just compile localy to know the value and than just hardcode it in test .
2. Squash+rebase some commits. Commit for clippy fixes, you actual fix for library, and tests fix.

[IddoPuff]

OK, I think that the stacktrace_structs and memory test are very flimsy since the addresses will change each compilation, and the stack trace can contain different functions in different versions of gcc. I will think of a more reliable test