Support for splitting output into multiple HTML files

[edwintorok]

Some documents can grow quite large (books, software documentation, etc.), and it is usual to split
the input/output into multiple files, while still having cross-references working correctly.
Splitting the input is not really necesary as editors can handle large files these days, and can be worked around by using a preprocessor like gpp or perhaps mpp if really needed.
Splitting the output is useful to improve page load times, reduce rendering stalls, reduce bandwidth usage, etc.

Lambcmd should support splitting the output into multiple files based on a configurable depth
(\part,\section,\subsection, or none at all).
Or -- if it is easier -- splitting based just on \part would be a good start: inserting a \part doesn't change numbering, and gives you control on where the splits happen.

[darioteixeira]

Let's keep this ticket open, though I'm rating this as a low priority feature, because you can always use a XML processor to split the document after the fact.