Move Blob's `seek` to an impl of std::io::Seek.
Move Blob's `seek` to an impl of std::io::Seek.

mikelodder7/rusqlcipher,mikelodder7/rusqlcipher,jgallagher/rusqlite,gwenn/rusqlite,gwenn/rusqlite,xinghun92/rusqlite,xinghun92/rusqlite,jgallagher/rusqlite,gwenn/rusqlite,xinghun92/rusqlite,jgallagher/rusqlite,mikelodder7/rusqlcipher