Change build system to rscons.

Rsconscript

@@ -0,0 +1,18 @@
+configure do
+  check_c_compiler
+  check_cxx_compiler
+  check_cfg package: "sdl2"
+  check_cfg package: "freetype2"
+end
+
+build do
+  Environment.new do |env|
+    env["CCFLAGS"] += %W[-Wall]
+    env["CXXFLAGS"] += %W[-std=gnu++14]
+    env["CPPPATH"] += glob("libs/glcxx/include", "libs/glm", "src")
+    env["CPPDEFINES"] += %W[GLCXX_GL_INCLUDE="GL3/gl3w.h"]
+    env["LIBS"] += %W[dl GL]
+    sources = glob("src/**/*.{c,cc}", "libs/glcxx/src/**/*.cpp")
+    env.Program("freetype2gl3", sources)
+  end
+end