adds nice explanatory images to the documentation of `graph.rs`.

* added links to online documentation, added black hat slides

* add spaces for codacy

* This commit improves the cwe_checker_to_ida tool. First, it fixes
issue #24. Second, it introduces some unit tests for
cwe_checker_to_ida. Third, cwe_checker_to_ida parses newer cwe checks
like cwe415 or cwe787. Forth, updated description of
cwe_checker_to_ida in README.md.