Removed link to outdated Cocoa Fundamentals doc
Sublime Text removed some trailing whitespace for me.
Add uber-important note from the Apple docs warning about function calls & NSAssert

  * https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Functions/Reference/reference.html#//apple_ref/c/macro/NSAssert
Merge pull request #2 from medington/master

Remove trailing whitespace and add important note to NSAssert section
bitmask operations

working with bitmasks (with multiple states allowed)
bitmask operations

set single bit to zero
Merge pull request #3 from senfi/patch-1

More bitmask operations
Code review
Contributors
Added objc.io and NSHipster references