add a default travis

.travis.yml

@@ -0,0 +1,24 @@
+language: c
+sudo: false
+cache:
+  directories:
+    - ~/arduino_ide
+    - ~/.arduino15/packages/
+git:
+  depth: false
+  quiet: true
+env:
+  global:
+     - ARDUINO_IDE_VERSION="1.8.7"
+     - PRETTYNAME="Adafruit BusIO Library"
+
+before_install:
+   - source <(curl -SLs https://raw.githubusercontent.com/adafruit/travis-ci-arduino/master/install.sh)
+
+script:
+   - build_main_platforms
+
+# Generate and deploy documentation
+after_success:
+  - source <(curl -SLs  https://raw.githubusercontent.com/adafruit/travis-ci-arduino/master/library_check.sh)
+  - source <(curl -SLs  https://raw.githubusercontent.com/adafruit/travis-ci-arduino/master/doxy_gen_and_deploy.sh)