Add PHP 5 Support

[ghost]

Modified char_mapping to support PHP 5. Since PHP 5 is lack of IntlChar, this version can only convert ASCII characters perfectly. Plain mode can work well in PHP 5.However, since PHP 5 doesn't support ("function_name")() to call functions, I added a mode called assert5 which added some extra characters to support eval in PHP 5.I have also updated the README file.

[splitline]

Awesome, thanks! But I insist on using only ([+.^]) to accomplish this (I want to keep those generated code fuckful XD).

Anyway, don't worry. Recently I found that we can use things like this in PHP 5.6+ (since spread syntax only support newer version), so we don't need to use $_='assert';!

call_user_func(...["assert","eval('echo 1; return 1;')"]);

I'll try it later, or maybe you can help me to achive this 😆