Add FindFrom extension trait to str to start searching at a byte offset.

This also moves the contents of `dedup.rs` into a shared module `extensions`.

src/extensions.rs

@@ -18,3 +18,16 @@ impl<T: PartialEq + Clone> Dedup<T> for Vec<T> {
         }
     }
 }
+
+/// Like `str::find`, but starts searching at `start`.
+pub(crate) trait FindFrom {
+    fn find_from(&self, needle: &Self, start: usize) -> Option<usize>;
+}
+
+impl FindFrom for str {
+    fn find_from(&self, needle: &Self, start: usize) -> Option<usize> {
+        self.get(start..)
+            .and_then(|s| s.find(needle))
+            .map(|i| i + start)
+    }
+}

src/main.rs

@@ -31,16 +31,16 @@ use serde_derive::Deserialize;
 
 mod cache;
 mod config;
-mod dedup;
 mod error;
+pub mod extensions;
 mod formatter;
 mod tokenizer;
 mod types;
 
 use crate::cache::{Cache, PageLookupResult};
 use crate::config::{get_config_dir, get_config_path, make_default_config, Config, MAX_CACHE_AGE};
-use crate::dedup::Dedup;
 use crate::error::TealdeerError::ConfigError;
+use crate::extensions::Dedup;
 use crate::formatter::print_lines;
 use crate::tokenizer::Tokenizer;
 use crate::types::{ColorOptions, OsType};