Added Hash#entries that returns an array of tuples
Run at_exit handlers when invoking exit
Allow executing raise inside macro (stops compilation, useful for example for method_missing)
Make sure to be able to compile Crystal even if there's no git repository in the current directory
Improved macro system error message
Fixed #158: more accurate way to determine which instance variables are nilable by checking which instance vars are read in calls from initialize.
Revert some changes in some initialize because of the previous commit