Add ability to convert between number bases

[tuhdo]

It would be nice if we are able to quickly convert between base 2, base 8 and base 16 on a number at point..

[knu]

It currently supports one way conversion from a decimal number, to base 2, 8 and 16.
https://github.com/knu/operate-on-number.el/blob/master/operate-on-number.el#L100-L103

Do you mean you want to convert a base 2/8/16 number at point to a decimal number? What prefixes/suffixes should it deal with, like 0x-, \x-, or -h?

[tuhdo]

Hex prefixes: 0x (in C), #x (in Emacs Lisp), # (in CSS).
Octal: In C, octal number is prefixed with 0, i.e. 0123 is 123 in octal.

I think if a number has the above prefixes, then it is fine for automatic conversion. If supply with prefix argument, users are asked for target base to convert to . In case of unable to identify the base, user is prompted to enter the number base and a target base to convert; then, operate-on-number convert to that base accordingly. By default, the target base should be decimal if user leaves the target base blank.

[knu]

To implement this properly, we must work out a way to detect the format to make sure it is kept after an operation: e.g. Incrementing 0x000f should result in 0x0010 instead of 16 or f.

By the way, I'm not sure if we should support zero-prefixed octal numbers by default. There are a bunch of zero-filled decimal and hexadecimal numbers out there.