#2 Allow substitution lists

[henspace]

When creating documents I often need to create
different versions for different different customers,
e.g same text but different names. I also have special
characters to embed into the documentation. e.g the
degrees symbol. To get around this I have amended a
version so that I can pass the appplication a command
lline argument to pick up a pair of files to use as
substitution lists. One file is used for HTML
substitutions and one for Latex. I tag the words I
want to substitute between ! and ; characters as this
is safe for both languages. So for example in the HTML
file I might have
!celsius; = ^oC
and in the Latex file
!celsius; = \ensuremath{^{\circ}}C
I also pass a build tag which gets added to the folders
so build 1 would go into HTML_1 and build 2 into HTML_2.

The way I have implemented this isn't very good as it
would be better done through the UI. But the concept
is, I think, generally useful.