Add 'load' javascript function for CLI, also create tests directory

How to test:

Type1:
~~~
$ ./build/mini
=> load
function load() { [native code] }
=> load('tests/version.js');
0.1.0
=> load('tests/help.js');
./mini <javascriptfile>
=>
~~~

Type2:
~~~
$ ./build/mini tests/version.js
0.1.0
$ ./build/mini tests/load.js
0.1.0
~~~