Initial conversion to Markdown
Fix Chapter 1 foreword
Chapter 1 cleanup

Deleted spurious spaces, made Harry's letter a blockquote. Not sure
whether to leave all the blockquotes italicized or leave that for
end-user styling.
Chapter 2 cleanup
Deleted spurious spaces from beginnings of italicized quotations in all files
Chapter 3 cleanup
Chapter 4 cleanup
Move Markdown files to subfolder