Add methods for aligning view edges to the center of other views.

[gshackles]

Thanks for the contribution! We're definitely starting to get into the territory of wondering how many more of these helpers we add before it's just too many, but I can see how these would be useful 😄

Can you add something to the sample app that shows them in action? That helps serve both as tests and also as examples for users of the library.

Thanks!

[Tyron18]

examples added