add SharedObject and SharedLibrary builders - close #8

build_tests/shared_library/Rsconsfile

@@ -0,0 +1,11 @@
+Rscons::Environment.new do |env|
+  env["CPPPATH"] << "src/lib"
+  libmine = env.SharedLibrary("libmine", Dir["src/lib/*.c"])
+  env.Program("test-shared.exe",
+              Dir["src/*.c"],
+              "LIBPATH" => %w[.],
+              "LIBS" => %w[mine])
+  env.build_after("test-shared.exe", libmine.to_s)
+  env.Program("test-static.exe",
+              Dir["src/**/*.c"])
+end