Add explanation of the distribution around the OR, and calculation of the SE(LogOR)

[chapb]

Add info about the OR, the log-normal distribution, and calculating the SE from a CI or P-value in the math and stats section. https://docs.iam.amr.pub/en/latest/10_reference/math_stats.html

Also, link to sawmill and make sure a "calculating SE from CI/p-val" is exported.