Update to 0.52.0

• Update COMMENT
• Update LICENSE
• Add LICENSE_FILE
• Remove PSUTIL option: psutil is no longer optional
• Allow concurrent installation (USE_PYTHON=concurrent)
• Update pkg-descr
• Add PyPI as primary WWW
• Update WWW
• Take maintainership

Changes: https://github.com/pythonprofilers/memory_profiler/commits/master