Enable lto in release versions.

lto makes exa slightly faster and much smaller. I specify the other
options to make them explicit.

Note: lto makes compiling take quite a bit longer.

Cargo.toml

@@ -22,6 +22,11 @@ bitflags = "0.1"
 default = [ "git" ]
 git = [ "git2" ]
 
+[profile.release]
+opt-level = 3
+debug = false
+lto = true
+
 [dependencies.git2]
 version = "0.1.13"
 optional = true