Documentation epub format

Hello devs,

I've given a try to the PostgreSQL documentation in epub format.

I must admit that there is a bit of a disappointement as far as the user
experience is concerned: the generated file is barely usable on an iPad2
with the default iBooks reader, which was clearly not designed for
handling a "4592" pages book (from its point of view).

The table of contents too much detailed, so it is long and slow to scan,
and there is no clear shortcut. Flipping pages in the documentation takes
ages (well, close to one second or more if I flip a few pages). Do not try
"search".

This seems to suggest that instead of generating one large ebook, the
build should generate a set of ebooks, say one for each part. At the
minimum, a less detailed toc could be more usable and help navigate the
huge contents.

--
Fabien.