chore: Fix swf doctests working directory

Rust 12-09 nightly changed the working dir of doctests to be the
workspace root instead of the subcrate root. This broke the
doctests for swf. Now do some setup to ensure the same working
directory on both stable and nightly.

cc rust-lang/cargo#8954

swf/src/read.rs

@@ -21,6 +21,7 @@ use std::io::{self, Read};
 ///
 /// # Example
 /// ```
+/// # std::env::set_current_dir(env!("CARGO_MANIFEST_DIR"));
 /// let data = std::fs::read("tests/swfs/DefineSprite.swf").unwrap();
 /// let swf = swf::read_swf(&data[..]).unwrap();
 /// println!("Number of frames: {}", swf.header.num_frames);
@@ -74,6 +75,7 @@ pub fn read_swf<R: Read>(input: R) -> Result<Swf> {
 ///
 /// # Example
 /// ```
+/// # std::env::set_current_dir(env!("CARGO_MANIFEST_DIR"));
 /// let data = std::fs::read("tests/swfs/DefineSprite.swf").unwrap();
 /// let swf_stream = swf::read_swf_header(&data[..]).unwrap();
 /// println!("FPS: {}", swf_stream.header.frame_rate);
@@ -367,6 +369,7 @@ impl<R: Read> Reader<R> {
     /// Reads the next SWF tag from the stream.
     /// # Example
     /// ```
+    /// # std::env::set_current_dir(env!("CARGO_MANIFEST_DIR"));
     /// let data = std::fs::read("tests/swfs/DefineSprite.swf").unwrap();
     /// let mut swf_stream = swf::read_swf_header(&data[..]).unwrap();
     /// while let Ok(tag) = swf_stream.reader.read_tag() {