button在开发中是个很常用的控件，为了美观有时我们会设置，button的BezlStyle，就是边框样式，一下是一些系统提供的button的边框样式,仅供大家参考：
typedef NS_ENUM(NSUInteger, NSBezelStyle) {
NSBezelStyleRounded = 1,
NSBezelStyleRegularSquare = 2,
NSBezelStyleDisclosure = 5,
NSBezelStyleShadowlessSquare = 6,
NSBezelStyleCircular = 7,
NSBezelStyleTexturedSquare = 8,
NSBezelStyleHelpButton = 9,
NSBezelStyleSmallSquare = 10,
NSBezelStyleTexturedRounded = 11,
NSBezelStyleRoundRect = 12,
NSBezelStyleRecessed = 13,
NSBezelStyleRoundedDisclosure = 14,
NSBezelStyleInline NS_ENUM_AVAILABLE_MAC(10_7) = 15,
};
NSBezelStyleRounded
NSBezelStyleRegularSquare
NSBezelStyleDisclosure
NSBezelStyleShadowlessSquare
NSBezelStyleCircular
NSBezelStyleTexturedSquare
NSBezelStyleHelpButton
NSBezelStyleSmallSquare
NSBezelStyleTexturedRounded
NSBezelStyleRoundRect
NSBezelStyleRecessed
NSBezelStyleRoundedDisclosure
NSBezelStyleInline
