Added standard Mustache specs tests suite.

The groups with failing tests are currently commented out (everything except
interpolation). The main reason for failures are due to the requirement that
standalone lines that contain nothing but whitespace be stripped from the
output.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "src/test/resources/specs"]
+        path = src/test/resources/specs
+        url = git://github.com/mustache/spec.git