Before merging in the oss-fuzz corpora from Google, there are some changes
to the fuzzer.
- Add a read corpus script, to display corpus files nicely.
- Change the behaviour of the fuzzer so that TLV parse failures all now
go down the same execution paths, which should reduce the size of the
corpora.
- Make unknown TLVs a failure to parse, which should decrease the size
of the corpora as well.
Closes#1881
