Use OsError when File::metadata fails (#50)

src/exceptions.rs

@@ -5,4 +5,3 @@ use pyo3::exceptions::PyException;
 
 create_exception!(cramjam, CompressionError, PyException);
 create_exception!(cramjam, DecompressionError, PyException);
-create_exception!(cramjam, CramjamError, PyException);

src/io.rs

@@ -6,7 +6,6 @@ use std::fs::{File, OpenOptions};
 use std::io::{copy, Cursor, Read, Seek, SeekFrom, Write};
 
 use crate::BytesType;
-use crate::exceptions::CramjamError;
 use numpy::PyArray1;
 use pyo3::class::buffer::PyBufferProtocol;
 use pyo3::prelude::*;
@@ -341,7 +340,7 @@ impl RustyFile {
         let meta = self
             .inner
             .metadata()
-            .map_err(|e| CramjamError::new_err(e.to_string()))?;
+            .map_err(|e| pyo3::exceptions::PyOSError::new_err(e.to_string()))?;
         Ok(meta.len() as usize)
     }
 }