Add support for flip row order BMP

[Tsuk1ko]

Refer to image-size/image-size#89

A BMP with flip row order can be made by Photoshop:

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One more thing I found these two functions were named incorrectly:

probe-image-size/lib/common.js

Lines 55 to 67 in 158c262

	exports.readUInt32LE = function (data, offset) {
	return data[offset] |
	(data[offset + 1] << 8) |
	(data[offset + 2] << 16) |
	(data[offset + 3] * 0x1000000);
	};
	exports.readUInt32BE = function (data, offset) {
	return data[offset + 3] |
	(data[offset + 2] << 8) |
	(data[offset + 1] << 16) |
	(data[offset] * 0x1000000);
	};

They actually read signed integers, not unsigned integers.