Don't wrap due to trailing space

The line wrapper considers trailing space part of a word, so it will bump words to the next line when they really would have fit.

This change tracks the amount of trailing space in the word so we can choose to only wrap when the word itself would overflow beyond the available width.

[Here is a document](https://braveleaf.com/jsbin/pdfkit-wrapping.pdf) that shows the same text rendered before and after this code change.