* add definitions for is_number and tie (by lemire)
* add fuzzer for element
* update fuzz documentation
* fix UB in creating an empty padded string
* don't bother null terminating padded_string, it is done by the std::memset already
* refactor fuzz data splitting into a separate class
This adds a fuzzer for at_pointer() which recently had a bug.
The #1142 bug had been found with this fuzzer
Also, it polishes the github action job:
cross pollinate the fuzzer corpora (lets fuzzers reuse results from other fuzzers)
use github action syntax instead of bash checks
only run on push if on master
Paul Dreik