[lucy-dev] Standalone documentation files

[Nick Wellnhofer]

Lucifers,

It would be nice to support standalone documentation files that work across 
all host languages. A hackish way that already works is to define empty inert 
classes with only a DocuComment. This approach is already used for 
Lucy::Docs::DevGuide and Lucy::Docs::FileLocking. The downsides are that this 
creates superfluous header files and that for lenghty documentation, it would 
be nice to work with plain Markdown that doesn't have to wrapped in C comments.

The problem with a plain .md file is you can't tell which parcel the 
documentation file belongs to. This piece of information is needed to organize 
the C documentation and for the custom URI scheme. But it should be easy to 
add this metadata with a `@parcel Lucy` directive, similar to the `@param` 
syntax for function documentation.

Another approach is to use some kind of "distribution" identifier that is 
unique across a single build and can be used for multiple parcels. We already 
have something similar (`boot_class`) for the Perl bindings, but I'd prefer to 
keep parcels completely separate regardless of how they're distributed and 
built. (I'd also like to have a separate .xs files for each parcels, for example.)

Thoughts?

Nick