[Minor] Fix security issues and add security documentation

[Minor] Fix security issues and add security documentation

- Fix command injection in configdump(): use list form open() instead of
backticks with string concatenation
- Fix ReDoS in ProcessLog(): escape regex metacharacters in symbol names
with \Q...\E when matching against log symbols
- Add SECURITY CONSIDERATIONS section to POD documenting trust assumptions
for map files, configuration, and log files