Improve error message for parsing errors

Currently we're logging things like:
> Record containing invalid integer: 'FN record missing for function top'
It's better to log them as:
> Parsing error: 'FN record missing for function top'

src/parser.rs

@@ -60,7 +60,7 @@ impl fmt::Display for ParserError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
             ParserError::Io(ref err) => write!(f, "IO error: {}", err),
-            ParserError::Parse(ref s) => write!(f, "Record containing invalid integer: '{}'", s),
+            ParserError::Parse(ref s) => write!(f, "Parsing error: '{}'", s),
             ParserError::InvalidRecord(ref s) => write!(f, "Invalid record: '{}'", s),
             ParserError::InvalidData(ref s) => write!(f, "Invalid data: '{}'", s),
         }