Add benchmark stage to CI

Author: tsolomko

.travis.yml

@@ -25,6 +25,20 @@ jobs:
       - swift test --filter BitByteDataTests.LsbBitWriterTests
       - swift test --filter BitByteDataTests.MsbBitWriterTests
       - swift build -c release # Check Release build just in case.
+    - stage: benchmark
+      if: NOT (tag IS present)
+      language: swift
+      os: osx
+      osx_image: xcode9.4
+      script:
+      - swift test -c release --filter BitByteDataTests.ByteReaderBenchmarks
+    - language: generic
+      os: linux
+      dist: trusty
+      install:
+      - eval "$(curl -sL https://gist.githubusercontent.com/kylef/5c0475ff02b7c7671d2a/raw/9f442512a46d7a2af7b850d65a7e9bd31edfb09b/swiftenv-install.sh)"
+      script:
+      - swift test -c release --filter BitByteDataTests.ByteReaderBenchmarks
     - stage: deploy
       if: tag IS present
       language: generic