Advanced logging system

- You can now define a custom `LogStyle`
- Added `warn()`, error(), `notice()` and `advancedLog()` to `FlxG`
- `warn()`, error(), `notice()` and `log()` support a variable amount of
paramaters. This means that to get an output of "X: 500 Y: 250", you no
longer need to seperate everything with plus signs (log("X: " + this.x +
" Y: " + this.y);), instead you can just have seperate paramters:
log("X: ", this.x, "Y:", this.y); which is more convenient and readable
- Updated all the existing error and warning messages previously using
log()