LibJS: Start building a JavaScript engine for SerenityOS :^)

I always tell people to start building things by working on the thing
that seems the most interesting right now. The most interesting thing
here was an AST + simple interpreter, so that's where we start!

There is no lexer or parser yet, we build an AST directly and then
execute it in the interpreter, producing a return value.

This seems like the start of something interesting. :^)

Libraries/LibJS/Makefile

@@ -0,0 +1,15 @@
+OBJS = \
+    AST.o \
+    Function.o \
+    Interpreter.o \
+    Object.o \
+    Value.o
+
+LIBRARY = libjs.a
+
+install:
+	mkdir -p $(SERENITY_BASE_DIR)/Root/usr/include/LibJS/
+	cp *.h $(SERENITY_BASE_DIR)/Root/usr/include/LibJS/
+	cp $(LIBRARY) $(SERENITY_BASE_DIR)/Root/usr/lib/
+
+include ../../Makefile.common