Introduce the concept of binding.

Introduce the concept of binding.

Bindings are in fact script interpretors. We can have several different
language bindings at the same time, with each registered at the compiling time
and loaded (initialized) dynamically at runtime. It's an bridge between
scripts and screen itself.

1. Rename the scripts struct to binding. Related functions are renamed too.
For example, LoadScripts() is now LoadBindings(); ScriptFInit() is now
FinalizeBindings().

2. Do not need to initialize the binding explicitly.

3. Reorganize the structure of script.c, grouping binding related stuffs
together.

4. Add myself to the copyright line of script.c.

5. Fully implement the logic of ScriptSource().