Add color to the logging output

[mkilgore]

The logging support added by #556 does not use colors, when viewed from an interactive output we should color the output to make it easier to read. Some things to consider:

• On Linux and Mac OS, we should use isatty() to determine whether to include colors or not (that way colors are not used if the result is being piped to a file or similar).
  • We should have an override environment variable to allow bypassing the isatty() check. NO_COLOR and FORCE_COLOR are the typical "standard" variables for this.
• Windows requires special handling:
  • For regular Console coloring we have to use the wincon.h API.
  • For Windows 10+, Terminal, and MinTTY we can use regular escape sequences like on Linux and Mac OS.
    • We'll need to check if isatty() still works on Windows. isValidCygwinPipe can probably complement it.