align word-wrap between `textarea` and overlay about poemdown

[connectuum]

most importantly, the use of   in place of simple space characters was disrupting the natural word-wrapping. the HTML conversion now avoids this replacement in single-space situations. the   symbol forces space character(s) to appear in HTML; typically HTML collapses multiple spaces into a single one.

by adding an overflow-wrap style to the overlay, we also handle scenarios where the text is so long that it must forcibly break.