If 'weblocks-webapp-public-files-path' is
nil (default), tries a number of strategies to determine a default
location of public files. First, an asdf system with the name of the
application ('weblocks-webapp-name') is searched for. If found, a
directory 'pub' is searched for in the parent directory of the asdf
file. If found, this directory is returned as the physical
value. Otherwise, 'weblocks.asd' is found, and the 'pub' folder in
that directory is returned.