replace commented fprintf with DBG_CTX
marshall column info
add column to Definition call sites
track location for references and referencedby

The hash key is now the file location(file:line:column).
Later on, this key is used to provide the reference location
to the consumers(xmlgen and sqlite3gen)
xmlgen: add attribute 'column' for 'location' tag
xmlgen: add attributes atline,atcol,infile for 'references' tag
sqlite3gen: generate sqlite3