Regarding documentation, comments in tens of .h files in third level directories are very user unfriendly, regardless of their quality (which seems fairly good). You need:

1) an overview of the available functionality, design choices, aspects that need feedback and contributions etc.

2) a guide of what headers every function or macro is located in (consider fragmenting headers less, possibly adding "umbrella" headers that just include a set of the current headers that is likely to be used together)

3) generated API docs in the web site.