Support hexadecimal and unicode escape sequences

[ta5een]

Summary

This issue applies to character and string literals. Currently, both of these literals only recognise simple escape sequences of a backslash and a certain character, for example \n. However, there will be cases where one may desire to input a Unicode or ASCII escape sequence, for example "\u{24}" or "\x24" for the dollar sign ($).

Possible methods of implementation

I'm not exactly sure how to approach this problem. I will look for possible ways to implement this feature as I learn more. For now, this issue will remain open as a reminder.