Set ALLLANG to install all the languages, otherwise set DOC_LANG
to just the languages (and encodings) you want to install.
Default to building the html-split (lots of small HTML files, with
links to go between them), html (one big honking HTML file), and plain
text versions of the documentation. Does not compress any of the docs
prior to doing the installation.
Testing and feedback: Jack O'Neill <jack@germanium.xtalwind.net>,
Cockups and typos: nik