Tweak spacing in README urls

Switches to use '[text] (link)' from '[text](link)' to make line
breaks less disruptive.
Remove file reference to asymptotics/introduction

The 'asymptotics' part of the book doesn't have an introduction. There
was a mistaken reference to an introduction.tex file that caused
compilation problems, so it has now been removed.
Merge branch 'master' into regression