moved headers folder ruby-2.1.0 to ruby-2.1.0-p0 to match what code expectations

if you want "declare a victory for now" like someone said on #27. here are the ruby 2.1.0 headers moved to the folder 2.1.0-p0.
I used these changes and I was able to compile and run the the debugger tests and they failed as expected with "dyld: lazy symbol binding failed: Symbol not found: rbvm_get_sourceline". By the way, they really also failed with ruby 2.0.0.