Travis: split build into jobs

- Change benchmarks build to use `cargo test --benches`. This runs the
  benchmarks and compiles faster than `cargo bench`.

Closes #169

.travis.yml

@@ -2,14 +2,14 @@ language: rust
 rust: nightly
 sudo: false
 
-before_script:
+jobs:
+  include:
+    - name: "Main"
+      script:
         - |
           RUN_CLIPPY=true
           rustup component add clippy --toolchain=nightly || RUN_CLIPPY=false
-
-script:
         - cargo test --all --all-features
-  - (cd benchmarks && cargo bench --no-run)
         - |
           if $RUN_CLIPPY; then
             CLIPPY_STATUS=0
@@ -18,3 +18,6 @@ script:
             done
             (exit $CLIPPY_STATUS)
           fi
+    - name: "Benchmarks"
+      script:
+        - (cd benchmarks && cargo test --benches)