feat(did-you-mean): gate it behind 'suggestions'

You can now disable the did-you-mean feature entirely, which also
removes the additional dependency it comes with.
Learn more about features and how to use them here:
http://doc.crates.io/manifest.html#the-[features]-section

Related to #103

Cargo.toml

@@ -13,11 +13,14 @@ keywords = ["argument", "command", "arg", "parser", "parse"]
 
 license = "MIT"
 
-[dependencies]
-strsim = "*"
-
 [features]
-default=[]
+default=["suggestions"]
+suggestions=["strsim"]
 
 # for building with nightly and unstable features
 unstable=[]
+
+[dependencies.strsim]
+version = "*"
+optional = true
+

src/app.rs

@@ -11,12 +11,14 @@ use args::{ ArgMatches, Arg, SubCommand, MatchedArg};
 use args::{ FlagBuilder, OptBuilder, PosBuilder};
 use args::ArgGroup;
 
+#[cfg(feature = "suggestions")]
 use strsim;
 
 /// Produces a string from a given list of possible values which is similar to 
 /// the passed in value `v` with a certain confidence.
 /// Thus in a list of possible values like ["foo", "bar"], the value "fop" will yield
 /// `Some("foo")`, whereas "blark" would yield `None`.
+#[cfg(feature = "suggestions")]
 fn did_you_mean<'a, T, I>(v: &str, possible_values: I) -> Option<&'a str> 
     where       T: AsRef<str> + 'a,
                 I: IntoIterator<Item=&'a T> {
@@ -35,6 +37,13 @@ fn did_you_mean<'a, T, I>(v: &str, possible_values: I) -> Option<&'a str>
     }
 }
 
+#[cfg(not(feature = "suggestions"))]
+fn did_you_mean<'a, T, I>(_: &str, _: I) -> Option<&'a str> 
+    where       T: AsRef<str> + 'a,
+                I: IntoIterator<Item=&'a T> {   
+    None
+}
+
 /// A helper to determine message formatting
 enum DidYouMeanMessageStyle {
     /// Suggested value is a long flag

src/lib.rs

@@ -348,6 +348,7 @@
 //!   - `Arg::new()` -> `Arg::with_name()`
 //!   - `Arg::mutually_excludes()` -> `Arg::conflicts_with()`
 //!   - `Arg::mutually_excludes_all()` -> `Arg::conflicts_with_all()`
+#[cfg(feature = "suggestions")]
 extern crate strsim;
 
 pub use args::{Arg, SubCommand, ArgMatches, ArgGroup};