Sensible return codes and Flush All

This release has two new improvements:

• omitting the qualifier in the flush command will flush all directories (not version or broadcast)
• sensible return codes are returned for scripting situation, with appropriate test coverage

Support ARM64 Linux architecture

• Supports aarch64 Linux architecture.

Minor bug fix release

Fixes minor issue #779

Minor improvements and performance enhancement

• Replace $(cat file) invocations with $(< file) for better performance.
• Use relative path for current symlink to version directory.
• Improve handling of secure curl downloads.
• Remove unused legacy bash workarounds