Added binary chop algorithm to speed up finding a string that fits.

[btwelch]

This pull request introduces a binary chop algorithm to significantly improve the search for the best-fit string size for a given container. Without this, using a character-by-character (blank-ellipses-separator) check would be very inefficient.

[kevindice]

This would help me out a lot. I've got an infinite scroll feed with each item using this directive. Performance is suffering a bit right now.