Add number->string function to lisp

[vinc]

Add a function in lisp to convert a number to a string, with an optional radix argument: (number->string number radix)

[vinc]

~
> lisp
MOROS Lisp v0.6.0

> (num->str 0xFFFF 16) # Hexadecimal
"FFFF"

> (num->str 0xFFFF 10) # Decimal
"65535"

> (num->str 0xFFFF 2) # Binary
"1111111111111111"

> (num->str 0xFFFF 1) # Error
Error: Expected radix in the range 2..37

> (num->str 0xFFFF) # Decimal by default
"65535"

> (num->str 256 16)
"100"

> (num->str 256 2)
"100000000"