* fuzz/get_ossfuzz_corpora: New file to download and merge corpora
* fuzz/*.in/*: New corpora
* fuzz/run-clang.sh: Updated to work with get_ossfuzz_corpora
* Makefile.am: Add target 'fuzz-coverage' to generate a coverage
report for fuzz targets.
* fuzz/Makefile: Add target 'fuzz-coverage'
* fuzz/coverage.sh: New script to call a fuzz target with each corpus.
* fuzz/libwget_metalink_parse_fuzzer.cc: Add check for max input length.
* fuzz/libwget_xml_parse_buffer_fuzzer.cc: Likewise
* fuzz/libwget_robots_parse_fuzzer.cc: Add comment
* fuzz/libwget_robots_parse_fuzzer.in/user_agent2: Amend for max coverage
* fuzz/main.c: selfmade __AFL_LOOP() returns 0 after first invocation.
* fuzz/libwget_memtohex.in: Rename to fuzz/libwget_memtohex_fuzzer.in
* fuzz/libwget_metalink_parse.in: Rename to fuzz/libwget_metalink_parse_fuzzer.in
* fuzz/libwget_robots_parse.in: Rename to fuzz/libwget_robots_parse_fuzzer.in
* fuzz/libwget_xml_parse_buffer.in: Rename to fuzz/libwget_xml_parse_buffer_fuzzer.in
* fuzz/libwget_xml_parse_buffer.options: Removed
* fuzz/libwget_metalink_parse_fuzzer.options: Removed