Set up continuous integration

Add Travis for OS X and Linux (Ubuntu), Appveyor for Windows builds.

.travis.yml

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+os:
+  - linux
+  - osx
+dist:
+  - xenial
+
+language:
+  - c++
+
+compiler:
+  - gcc
+  - clang
+
+addons:
+  apt:
+    sources:
+      - sourceline: 'deb http://download.opensuse.org/repositories/home:/selmf/xUbuntu_16.04/ /'
+        key_url: 'https://download.opensuse.org/repositories/home:selmf/xUbuntu_16.04/Release.key'
+      - sourceline: 'ppa:kubuntu-ppa/backports'
+    packages:
+      - qt-default
+      - qt5-qmake
+      - qtbase5-dev
+      - qtmultimedia5-dev
+      - libpoppler-qt5-dev
+      - qtscript5-dev
+      - libqt5opengl5-dev
+      - libglu1-mesa-dev
+      - libunarr-dev
+      - qtdeclarative5-dev
+  homebrew:
+    packages:
+      - qt
+
+before_script:
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]];
+    then brew link qt --force;
+    qmake CONFIG+=unarr;
+    fi
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]];
+    then QT_SELECT=qt5 qmake CONFIG+=unarr;
+    fi
+
+script: make

appveyor.yml

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+image: Visual Studio 2017
+
+environment:
+  matrix:
+    - platform: x86
+      QT5: C:\Qt\5.12.1\msvc2017
+      VCVARS: '"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars32.bat"'
+    - platform: x64
+      QT5: C:\Qt\5.12.1\msvc2017_64
+      VCVARS: '"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"'
+
+before_build:
+  - set PATH=%QT5%\bin;%PATH%
+  - call %VCVARS%
+  - cd %APPVEYOR_BUILD_FOLDER%
+  - qmake CONFIG+=unarr
+
+build_script:
+  - cd %APPVEYOR_BUILD_FOLDER%
+  - nmake