Fixes, small changes + `null` + `array_length`

- Fixed `Wrong type in call to (...)` error
- Fixed `Cannot create an any-typed array!` error
- Fixed `string to char` assignment
- Fixed string arrays
- Fixed parsing escape chars
- Fixed types in including
- Fixed `mov` param type check
- Small change in expression parser
- New constant: `null`
- Added hexadecimal numbers parsing (prefix `0x`)
- Implemented `array_length`