Support OSLog; drop CleanroomASL; add back color-coding

• Supports Apple's new Unified Logging System aka OSLog aka os_log
• Removes the CleanroomASL dependency — CleanroomLogger is now dependency-free!
• Adds back color coding; we lost this when XcodeColors was wiped out by Xcode 8. Although it is now in a different form:

◽️ Verbose messages are tagged with a small gray square — easy to ignore
◾️ Debug messages have a black square; easier to spot, but still de-emphasized
🔷 Info messages add a splash of color in the form of a blue diamond
🔶 Warnings are highlighted with a fire-orange diamond
🛑 Error messages stand out with a red stop sign — hard to miss!