unixbench release 6.0.0

We are pleased to announce the release of UnixBench 6.0.0, a significant milestone since version 5.1.3. This release delivers major improvements to the build system, enhanced support for modern architectures such as ARM64/Risc-V, improved platform compatibility, and updated documentation.

Build System Modernization
Introduced support for custom compiler flags via the UB_GCC_OPTIONS environment variable.
Architecture-aware compiler optimization flags (e.g., -march=native, -mcpu=native) for x86, ARM, RISC-V, PowerPC, etc.
Cleaner and more portable Makefile, compatible with GNU Make.
Improved separation of CFLAGS and LDFLAGS with autodetection of platform-specific needs.

Platform & Architecture Enhancements
Added detailed ARM64 CPU detection with support for multiple vendors (ARM, Ampere, Cavium, Apple, etc.).
Improved support for macOS using sysctl and Darwin-specific logic.
Portable CPU core detection using nproc, getconf, and fallback logic.
Improved fallback behavior when /proc/cpuinfo is unavailable.

System Detection and Configuration
Run script now uses FindBin for consistent directory resolution.
Default directories (pgms, results, tmp) are created automatically if missing.
Log file names can now be customized via UB_OUTPUT_FILE_NAME environment variable.
Improved cross-platform compatibility and shell behavior.

Documentation and Licensing
Added official GPL v2 license file.
Rewritten and modernized README.md in Markdown format.
Clear explanation of each benchmark test and history of the project.
Updated contributor credits and project guidelines.

Performance Comparison Guidelines
To ensure meaningful and repeatable benchmarking results, it is strongly recommended to maintain consistency in the following areas when comparing performance
Operating System: Use the same OS distribution and version.
Compiler Options: Use consistent compiler flags across test cases (e.g., -O3, -march=native).
System Configuration: Ensure similar runtime environments (CPU governor, I/O scheduler, background load).
Benchmark Version: Always compare results using the same version of UnixBench