Make the rav1e command optional

Cargo.toml

@@ -8,9 +8,11 @@ autobenches = false
 autobins = false
 
 [features]
-repl = ["rustyline"]
+repl = ["rustyline", "binaries"]
 comparative_bench = []
 decode_test = ["bindgen"]
+binaries = ["y4m"]
+default = ["binaries"]
 
 [dependencies]
 bitstream-io = "0.6"
@@ -18,7 +20,7 @@ clap = "2"
 libc = "0.2"
 rand = "0.5"
 rustyline = { version = "1", optional = true }
-y4m = "0.3"
+y4m = { version = "0.3", optional = true }
 enum-iterator-derive = "0.1.1"
 backtrace = "0.3"
 num-traits = "0.2"