Fuzzer statistics

[GrosQuildu]

Each fuzzer executor (frontend) implements populate_stats method that changes fuzzer-specific output information to the uniform one. That is, it's populate self.stats dictionary.

Currently only AFL provides reasonable amount of runtime informations that are easily accessible and therefore used by the deepstate. Also we scan CRASH_DIR and count amount of crashes found. But other tools needs more research and engineering work to get stats from them.

For some more info, see #326 .

TODO:

• fix for libFuzzer statistic parsing. We parse it's stdout. Unfortunately deepstate transforms fuzzer output to hardly readable. So only exec/s are successfully retrieved (not units or cov).
• map libFuzzer (and other) statistic to the AFL one (or rename keys in self.stats dict)
• research about what statistic can we get from Honggfuzz, Angora and Eclipser
• implementation, based on the point above