Add detection of projects
  - subdirectories of research which include a Readme.md file
Add a flag FEELPP_ENABLE_PROJECT_DOCUMENTAION per file
Update Doxygen.in
  - eventually add directories to search for project doc if requested
  - remove */research/* from exclude
Add pages.in
  - generate pages.doc with eventually subpages for projects
  - pages.doc has been added to .git-ignore
Merge branch 'develop' of github.com:feelpp/feelpp into develop