Implement schema validation

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "tests/googletest"]
 	path = tests/googletest
 	url = https://github.com/google/googletest
+[submodule "extern/valijson"]
+	path = extern/valijson
+	url = https://github.com/tristanpenman/valijson

CMakeLists.txt

@@ -46,7 +46,9 @@ find_package(zlib)
 find_package(bzip2)
 
 set( INCLUDE_DIR include )
+set( VALIJSON_INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/extern/valijson/include" )
 include_directories( ${INCLUDE_DIR} ${YAML_INCLUDE_DIR} )
+include_directories( SYSTEM ${VALIJSON_INCLUDE_DIR} )
 
 set(asdf_c_flags ${CMAKE_C_FLAGS})
 set(asdf_cxx_flags ${CMAKE_CXX_FLAGS})
@@ -63,6 +65,9 @@ set_target_properties(asdf-cpp PROPERTIES
   COMPILE_FLAGS "${asdf_c_flags} ${asdf_cxx_flags}"
 )
 
+add_executable( validator src/validation.cpp )
+target_link_libraries( validator yaml-cpp )
+
 if (${ZLIB_FOUND})
     target_compile_definitions(asdf-cpp PRIVATE HAS_ZLIB=1)
     target_include_directories(asdf-cpp PRIVATE ${ZLIB_INCLUDE_DIRS})