penepma_calc_k_ratio: Calculate the k-ratio from penepma intensities
In jrminter/rpemepma: Processing of data from PENEPMA simulations using R

Calculate the k-ratio for a desired transition from R tibbles that contain intensity data. Also compute the uncertainty and relative uncertainty.

1 2	penepma_calc_k_ratio(str_samp, str_kr, tib_unk, tib_std, z, s0, s1, n_rnd = 5)

`str_samp`	A string to describe the sample. Ex: "200 nm C on Fe"
`str_kr`	A string to describe the K-ratio Ex: "C Ka"
`tib_unk`	A tibble containing the penepma intensity data for the unknown.
`tib_std`	A tibble comtaining the penepma intensity data for the standard.
`z`	The atomic number for the element for the K-ratio. Ex: 6 for C.
`s0`	The number for the originating shell from Table 7.2. Ex: 1 for K.
`s1`	The number for the filling shell from Table 7.2. Ex: 4 for L3.
`n_rnd`	The number of digits to round values. Default: 5.