Logging: add XLFacility

# XLFacility

* Drop-in replacement of `NSLog()` along with trivial to use macros to log messages anywhere in your app without impacting performance
* Support a wide variety of logging destinations aka "loggers"
* Customizable logging formats
* Modern, clean and compact codebase fully taking advantage of the latest Obj-C runtime and Grand Central Dispatch
* Easy to understand architecture with the ability to write custom loggers in a few lines of code
* No dependencies on third-party source code
* Available under a friendly [New BSD License](LICENSE)

Built-in loggers:
* Standard output and standard error
* [Apple System Logger](https://developer.apple.com/library/mac/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/LoggingErrorsAndWarnings.html)
* Local file
* Local [SQLite](http://www.sqlite.org/) database
* Telnet server which can be accessed from a terminal on a different computer to monitor log messages as they arrive
* HTTP server which can be accessed from a web browser on a different computer to browse the past log messages and see live updates
* Raw TCP connection which can send log messages to a remote server as they happen
* User interface logging window overlay for OS X & iOS apps

Requirements:
* OS X 10.7 or later (x86_64)
* iOS 5.0 or later (armv7, armv7s or arm64)
* ARC memory management only