Support file extensions other than .xml and .dita
Add src attribute to job configuration

The src is the absolute URI to the source document for a fileinfo.
Processing has been changed to rely on this and contains initial code
for customising temporary file URIs.
Separate temp file name generator to a separate class
Refactor uplevels to support alternative temp directory names

Update uplevels processing to allow generating e.g. flattened temp
directory structures.
Accept all non-DITA or image references #1687

All references from image elements are treated as images references
without configures file extension. All references to non-DITA files
are processed without configured file extension.
Fix common attribute procession in dlentry
Merge README updates #1825
Remove deprecated error messages #1800