doc: improve Sign/Verify examples and docs
- Use complete examples that can be pasted and run as-is
- Move note about algorithm to the functions it applies to
- Uncapitalize inconsistence use of "Class"
- Use both EC and RSA keys in the examples
- Note that hash and digest are two names for the same algorithms
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines