add description + URL per directory; add summary table in Markdown

See merge request pub/open-source-case-studies!23

[x509-parser] add E-ACSL target; add test DER certificate

See merge request pub/open-source-case-studies!22

Note: several "ok" tests still contain warnings; in some cases, they seem
inevitable, but others can be improved by adding C stubs, ACSL annotations,
or improving the precision in other ways. They may also contain real bugs
which have not yet been patched.

Improve miniz

See merge request pub/open-source-case-studies!18

sync with frama-c master; fix papabench's math.h inclusion

See merge request pub/open-source-case-studies!19

[miniz] add more examples as use cases

See merge request pub/open-source-case-studies!17

[c-testsuite] add new case study

See merge request pub/open-source-case-studies!13