Add global verbose flag that prints more information about installation progress and errors

[interstateone]

This should involve expanding Logging.log with different logging levels, like debug, info, warn and error. A global log level would determine which log messages were actually output. Increasing log levels would print fewer, higher-priority messages. The default log level would be info, and the current output should migrate to the info level.

A new global -v/--verbose flag would change the log level to debug. This should output more information, like network request headers and bodies, so that users can provide more meaningful bug reports and we can more easily troubleshoot issues.

Colors should be set for the warn and error levels in one place, instead of at each Logging.log call site. Errors should also be sent to STDERR instead of STDOUT.

[skizzo]

This would be really handy, any updates on this? I can't get xcodes to work, see this issue: #314