Updated changelog for 0.7.5 release
Updated changelog for 0.7.5 release

burakbostancioglu/marathon-python,drewrobb/marathon-python,thefactory/marathon-python,thefactory/marathon-python,drewrobb/marathon-python,fengyehong/marathon-python,fengyehong/marathon-python,burakbostancioglu/marathon-python