refactor ~ replace deprecated trim_{left,right}... with trim_{start,end}...

- `trim_{start,end}{,_matches}` stabilized in rust v1.30.0
- `trim_{start,end}{,_matches}` deprecated (with compiler warnings) in rust v1.33.0

+ requires MinSRV >= v1.30.0

* ref: https://github.com/rust-lang/rust/blob/master/RELEASES.md

src/fmt/parasplit.rs

@@ -436,7 +436,7 @@ impl<'a> ParaWords<'a> {
     fn create_words(&mut self) {
         if self.para.mail_header {
             // no extra spacing for mail headers; always exactly 1 space
-            // safe to trim_left on every line of a mail header, since the
+            // safe to trim_start on every line of a mail header, since the
             // first line is guaranteed not to have any spaces
             self.words.extend(
                 self.para

src/pwd/pwd.rs

@@ -29,7 +29,7 @@ pub fn absolute_path(path: &Path) -> io::Result<PathBuf> {
         path_buf
             .as_path()
             .to_string_lossy()
-            .trim_left_matches(r"\\?\"),
+            .trim_start_matches(r"\\?\"),
     ).to_path_buf();
 
     Ok(path_buf)