Add basic gitignore functionality

No support for wildcards and exact matches might screw up nested
directories. The Globbing functionality seems like its going to be a
pain to properly match up.

src/config.rs

@@ -6,6 +6,7 @@ pub struct Config {
     pub pattern: String,
     pub ignore_case: bool,
     pub path: String,
+    pub use_gitignore: bool,
 }
 
 impl Config {
@@ -28,7 +29,12 @@ impl Config {
                 Arg::with_name("path")
                     .help("Path to search in")
                     .index(2)
-                    .default_value("."),
+                    .default_value(""),
+            )
+            .arg(
+                Arg::with_name("gitignore")
+                    .long("no-gitignore")
+                    .help("Include results that are specified in .gitignore"),
             )
             .get_matches();
 
@@ -36,6 +42,7 @@ impl Config {
             pattern: String::from(matches.value_of("pattern").unwrap()),
             ignore_case: matches.is_present("ignore case"),
             path: String::from(matches.value_of("path").unwrap()),
+            use_gitignore: !matches.is_present("gitignore"),
         }
     }
 }