import in, elseif, if true, if false, any

Thanks to everyone who contributed their ideas, a selection of proposed new syntaxes are now added

| js/c++ | wenyan | issue | |-|-|-| | continue | 乃止是遍 | #392 | | else if | 或若 | #365 | | if (ans) { | 若其然者 | #513 | | if (!ans) { | 若其不然者 | ditto | | auto | 元 | #486 | | require('path/to/something') | 吾嘗觀「「某樓」」中「「某閣」」中「「某書」」之書。 | #475 |

refer to #519 for more details