Removed the test binary from the repository

Obviously, this file does not belong here and was accidentally added
Added new macro: AS_UINT8

Although macros obscure code, I chose to add this macro for now because
it reduces verbosity of often-repeated code.
The macro first clamps down a function result to a max value of 255,
and then performs a cast to uint8_t.
The need for the macro arose after I found that i forgot to clamp the output
of the Sobel magnitude result.
added Prewitt operator
Added another macro to convert function values to uint8_t

TO_2D_UINT8_LAMBDA creates a lambda expression which aleviates the
need to a special function just for this conversion.
I am still debating whether these macros are good or bad.  Personally,
I don't like it when code is obfuscated because of macros hiding what's
really going on.  On the other hand, the full code is hard to read and
repeats often.
added an example of using the prewitt operator
added another macro
added support for grayscale/color for gaussian_3x3
added gradient direction calculation, and started canny implementation
continued the ever-growing wish list