Implement bitwise negation on numeric types

[sjbarag]

RBI supports bitwise negation of integers (and possibly floating-point/double values; needs confirmation), but brs currently doesn't. Let's make that work! Some details from a comment on a PR:

' in RBI
print not  0 ' => -1
print not  1 ' => -2
print not -1 ' =>  0
print not  2 ' => -3
print not -2 ' =>  1

which looks like RBI is using a two's complement representation for numbers and does something slightly unexpected with it. not someInteger in RBI seems to take someInteger, convert to a binary representation, perform a bitwise negation on it (all 0s become 1s, all 1s become 0s), then convert back to a decimal representation in the Two's complement understanding. So for not 0 (using just 4-bits for now because I'm lazy), we have:

not 0 (decimal) == not 0b0000 == 0b1111 == -1 (decimal in two's complement)

How strange! In the not 2 * 3 example, we get:

not (2 * 3) == not 6 (decimal) == not 0b0110 == 0b1001 == -7 (decimal in two's complement)