Added cache support for 'travis' builds.

Also refactored config to make it a bit cleaner.

Author: MrPointer

.travis.yml

@@ -1,11 +1,17 @@
+if: branch != feature/appveyor-ci
 language: cpp
 os:
 - linux
 - osx
 env:
-- ARDUINO_SDK_VERSION=1.6.10
-- ARDUINO_SDK_VERSION=1.8.7
-if: branch != feature/appveyor-ci
+  global:
+  - ARDUINO_SDK_BASE_PATH=/home/travis/arduino-sdk/arduino
+  matrix:
+  - ARDUINO_SDK_VERSION=1.6.10
+  - ARDUINO_SDK_VERSION=1.8.7
+cache:
+  directories:
+  - $ARDUINO_SDK_BASE_PATH-$ARDUINO_SDK_VERSION
 addons:
   apt:
     packages:
@@ -14,23 +20,25 @@ addons:
     - avrdude
     - cmake
 before_install:
+- sdk_path="$ARDUINO_SDK_BASE_PATH-$ARDUINO_SDK_VERSION"
+- mkdir -p "$sdk_path"
+- cd "$sdk_path/.." # Get to arduino-sdk
 - |
   if [[ $TRAVIS_OS_NAME == linux ]]; then
-    export ARDUINO_SDK_FILE="arduino-$ARDUINO_SDK_VERSION-linux64.tar.xz"
+    sdk_file="arduino-$ARDUINO_SDK_VERSION-linux64.tar.xz"
   else
-    export ARDUINO_SDK_FILE="arduino-$ARDUINO_SDK_VERSION-macosx.zip"
+    sdk_file="arduino-$ARDUINO_SDK_VERSION-macosx.zip"
   fi
-- wget "https://downloads.arduino.cc/$ARDUINO_SDK_FILE" -O "$ARDUINO_SDK_FILE"
-- mkdir arduino-sdk
+- wget "https://downloads.arduino.cc/$sdk_file" -O "$sdk_file"
 - |
   if [[ $TRAVIS_OS_NAME == linux ]]; then
-    tar xf "$ARDUINO_SDK_FILE" -C arduino-sdk --strip-components 1
-    export ARDUINO_SDK_PATH="$PWD/arduino-sdk"
+    tar xf "$sdk_file" --strip-components 1
   else
-    unzip "$ARDUINO_SDK_FILE" "Arduino.app/Contents/Java/*" -d arduino-sdk
-    export ARDUINO_SDK_PATH="$(pwd)/arduino-sdk/Arduino.app/Contents/Java"
+    unzip "$sdk_file"
   fi
+- export ARDUINO_SDK_PATH="$sdk_path"
 install:
+- cd "$TRAVIS_BUILD_DIR"
 - mkdir build
 - rm -rf build/*
 - cd build/