Wrap long lines
This commit wraps long lines in the Markdown source files. The main motivation for this is to make it easier to view changes in Git commits. Git shows line-by-line changes, so if a line contains an entire paragraph, it'll be hard to see what has changed. Most lines are now wrapped around the 80-character mark. This makes it much easier to view changes in Git. For some pages, this commit extracts link targets to the bottom of the page in order to allow for more sensible line wrapping. The content of pages is not changed.