Enable small_rng feature requirement for each benchmark

Not ideal but seems to work; see: rust-lang/cargo#6945

Author: dhardy

Cargo.toml

@@ -14,6 +14,7 @@ keywords = ["random", "rng"]
 categories = ["algorithms", "no-std"]
 build = "build.rs"
 exclude = ["/utils/*", "/.travis.yml", "/appveyor.yml", ".gitignore"]
+autobenches = true
 
 [badges]
 travis-ci = { repository = "rust-random/rand" }
@@ -83,6 +84,26 @@ rand_distr = { path = "rand_distr", version = "0.1" }
 [build-dependencies]
 autocfg = "0.1"
 
+[[bench]]
+name = "distributions"
+path = "benches/distributions.rs"
+required-features = ["small_rng"]
+
+[[bench]]
+name = "generators"
+path = "benches/generators.rs"
+required-features = ["small_rng"]
+
+[[bench]]
+name = "misc"
+path = "benches/misc.rs"
+required-features = ["small_rng"]
+
+[[bench]]
+name = "seq"
+path = "benches/seq.rs"
+required-features = ["small_rng"]
+
 [package.metadata.docs.rs]
 all-features = true