fix bugs in lib/rawmerge.hpp: merge_channels(...) and improve example.py

- raweat.hpp: find_markers(): properly (re)adjust valid_ flag when doing multiple conversion
- rawmerge.hpp: improve logging, merge_channels(): add condition to avoid range error in vector
- example.py: obtain return flag from add_channel(), write csv output from parquet table
- main.cpp: return to pure raw_eater test version

lib/raweat.hpp

@@ -251,7 +251,7 @@ public:
 
     // check validity of format
     // assert ( totalmarksize > 0 && "didn't find any predefined marker => probably not a valid .raw-file" );
-    if ( totalmarksize < 100 ) valid_ = false;
+    valid_ = ( totalmarksize < 100 ) ? false : true;
   }
 
   // display content of found markers