Make the engine to return csv string records as documents and headers

src/heed_codec/csv_string_record_codec.rs

@@ -0,0 +1,26 @@
+use std::borrow::Cow;
+use csv::{StringRecord, Writer, ReaderBuilder};
+
+pub struct CsvStringRecordCodec;
+
+impl heed::BytesDecode<'_> for CsvStringRecordCodec {
+    type DItem = StringRecord;
+
+    fn bytes_decode(bytes: &[u8]) -> Option<Self::DItem> {
+        let mut reader = ReaderBuilder::new()
+            .has_headers(false)
+            .buffer_capacity(bytes.len()) // we will just read this record
+            .from_reader(bytes);
+        reader.records().next()?.ok() // it return an Option of Result
+    }
+}
+
+impl heed::BytesEncode<'_> for CsvStringRecordCodec {
+    type EItem = StringRecord;
+
+    fn bytes_encode(item: &Self::EItem) -> Option<Cow<[u8]>> {
+        let mut writer = Writer::from_writer(Vec::new());
+        writer.write_record(item).ok()?;
+        writer.into_inner().ok().map(Cow::Owned)
+    }
+}

src/heed_codec/mod.rs

@@ -1,5 +1,7 @@
+mod csv_string_record_codec;
 mod roaring_bitmap_codec;
 mod str_beu32_codec;
 
+pub use self::csv_string_record_codec::CsvStringRecordCodec;
 pub use self::roaring_bitmap_codec::RoaringBitmapCodec;
 pub use self::str_beu32_codec::StrBEU32Codec;