Add tasks - close #139

build_tests/library/Rsconscript

@@ -1,4 +1,4 @@
-build do
+default do
   Environment.new(echo: :command) do |env|
     env.Program('library.exe', ['lib.a', 'three.c'])
     env.Library("lib.a", ['one.c', 'two.c'], 'CPPFLAGS' => ['-Dmake_lib'])