add crc checksums to sstables (#28)

Author: thomasjungblut

_examples/proto/hello_world.pb.go

@@ -5,9 +5,10 @@ option go_package = "github.com/thomasjungblut/go-sstables/sstables/proto";
 message IndexEntry {
     bytes key = 1;
     uint64 valueOffset = 2;
+    uint64 checksum = 3; // a golang crc-64 checksum of the respective dataEntry
 }
 
-// deprecated, it's unncessary overhead to marshal the bytes once more
+// deprecated, it's unnecessary overhead to marshal the bytes once more
 message DataEntry {
     bytes value = 1;
 }
@@ -20,4 +21,5 @@ message MetaData {
     uint64 indexBytes = 5;
     uint64 totalBytes = 6;
     uint32 version = 7; // currently version 1, the default is version 0 with protos as values
+    uint64 skippedRecords = 8;
 }