Support macros to get project name and project web URL

In Markdown files '@PROJECT@' and '@PROJECT_URL@' can now be used as
placeholders for the name and the web URL of the project from which
the documentation is shown.

Change-Id: I24fac86b194847d4bc1df5de2387f6d88e68c648
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>