stabilize path names in html output

[C. Michael Pilato]

Max Bowsher wrote:

> Regarding the location of example repositories, and the location of 
> the binaries...
> Is it desirable to allow the builder of the book to specify custom 
> substitutions at build time?
>
> My worry is that this may make it hard to control the line length in 
> command line demo sections.

No, sir.  For the reason listed, as well as for the sheer benefit of not 
going out of our way to facilitate a situation where copies of the book 
all over the 'Net have differences like that.  Consistency is all good.