Only compress metadata if resulting in smaller size

[wcampbell0x2a]

The size of the compressed bytes should be compared to the size of the uncompressed bytes. The following TODO shows the position of one of the checks.

diff --git a/src/metadata.rs b/src/metadata.rs
 index da6af38..cbd9969 100644
 --- a/src/metadata.rs
 +++ b/src/metadata.rs
 @@ -77,6 +77,8 @@ impl Write for MetadataWriter {
                  self.block_size,
              )?;

 +            // TODO: check if compressed bytes is < uncompressed bytes
 +
              // Metadata len + bytes + last metadata_start
              self.metadata_start += 2 + b.len() as u32;
              trace!("new metadata start: {:#02x?}", self.metadata_start);

The length would need to be updated when written to the block, as right now it assumes it will always be compressed.

[rbran]

#250 should solve this