Add CMake build to Travis config.

.travis.yml

@@ -1,5 +1,14 @@
+env:
+  matrix:
+    - JANSSON_BUILD_METHOD=cmake JANSSON_CMAKE_OPTIONS="-DJANSSON_TEST_WITH_VALGRIND=ON" JANSSON_EXTRA_INSTALL="valgrind"
+    - JANSSON_BUILD_METHOD=autotools
 language: c
 compiler:
   - gcc
   - clang
-script: autoreconf -f -i && CFLAGS=-Werror ./configure && make check
+install:
+  - sudo apt-get update -qq
+  - sudo apt-get install -y -qq cmake $JANSSON_EXTRA_INSTALL
+script:
+  - if [ "$JANSSON_BUILD_METHOD" = "autotools" ]; then autoreconf -f -i && CFLAGS=-Werror ./configure && make check; fi
+  - if [ "$JANSSON_BUILD_METHOD" = "cmake" ]; then mkdir build && cd build && cmake .. $JANSSON_CMAKE_OPTIONS && cmake --build . && ctest --output-on-failure; fi