Authored by Jonas Budelmann

Update CHANGELOG.md

v0.3.0
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* added `- (NSArray *)mas_updateConstraints:(void(^)(MASConstraintMaker *))block` which will update existing constraints if possible, otherwise it will add them. This makes it easier to use Masonry within the UIView `- (void)updateConstraints` method which is the recommended place for adding constraints by apple.
* added `- (NSArray *)mas_updateConstraints:(void(^)(MASConstraintMaker *))block` which will update existing constraints if possible, otherwise it will add them. This makes it easier to use Masonry within the `UIView` `- (void)updateConstraints` method which is the recommended place for adding/updating constraints by apple.
* Updated examples for iOS7, added a few new examples.
* Added -isEqual: and -hash to MASViewAttribute @CraigSiemens.
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* Added -isEqual: and -hash to MASViewAttribute [CraigSiemens].
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