Resolution calculation is wrong

[biochem-fan]

It looks that calculation of spot resolution is wrong.
The correct formula is d = lambda / 2 / sin(theta), while the code calculates lambda / sin(2 theta).
The variable "sintheta" is actually sin(2 theta).

For small theta, sin(2 theta) is close to 2 sin(theta), so the error is not very big. Is this intended approximation?

https://github.com/antonbarty/cheetah/blob/master/source/libcheetah/src/peakfinders.cpp#L200