Emit single-quoted strings instead of double-quoted. Closes GH-5

In C, single-quotes are for single character literals, double-quotes for
strings, but in JavaScript, both are for strings. Common style
convention for JavaScript uses single-quotes, so use them here too.

hello.c

@@ -6,7 +6,7 @@ int main(int argc, char **argv) {
     const double pi = 3.14159;
     static char *s = "foo";
 
-    printf("Hello, world!\n");
+    printf("Hello, world's!\n");
 
     if (a == 2) exit(1);
 

js_generator.py

@@ -37,6 +37,9 @@ def generic_visit(self, node):
             return ''.join(self.visit(c) for c_name, c in node.children())
 
     def visit_Constant(self, n):
+        # JS: single-quoted strings by convention
+        if n.value.startswith('"') and n.value.endswith('"'):
+            return "'%s'" % (n.value[1:-1].replace("'", "\\'"))
         return n.value
 
     def visit_ID(self, n):
@@ -141,6 +144,7 @@ def visit_DeclList(self, n):
         return s
 
     def visit_Typedef(self, n):
+        # JS: no typedef
         s = ''
         #if n.storage: s += ' '.join(n.storage) + ' '
         #s += self._generate_type(n.type)