Preserve whitespace in poems

[drewrey]

"[White space] is an active ingredient in poetic communication", so Virgil now preserves it.

I tried both pre and pre-wrap, but I found the former to better preserve the structure of the poem. In particular, when shrinking the size of my browser to where a horizontal scroll bar was necessary:

• pre deferred to a scrollbar immediately
• pre-wrap restructured the poem by trimming leading white space before introducing a scroll bar

Perhaps this is the distinction implied here for pre-wrap:

Lines are broken... as necessary to fill line boxes.