Define _ewf*, calling libewf_* to open/read/close EWF filesets
Implement EWFSource, wrapping _ewf* calls to open/read/write an EWF fileset
List supported EWF formats
Detect source type in main, use EWF format when supported format detected
Use source.__str__ for output, format EWF source to include first and last parts
Update README.md to include information on EWF support