growth_parameters: Calculate growth parameters
In EricEdwardBryant/screenmill: Tools for working with ScreenMill data

Calculates colony growth parameters by fitting a smooth growth curve using smooth.spline.

1	growth_parameters(time, size, ...)

`time`	Numeric - time of growth.
`size`	Numeric - size of colony.
`...`	Further arguments passed to `smooth.spline`.

Returns a data frame with the following parameters derived from the fit curve:

A	Maximum growth.
A_t	Time at maximum growth.
mu	Maximum growth rate.
mu_t	Time at maximum growth rate.
mu_y	Growth at maximum growth rate.
lambda	Lag phase (x-intercept of line tangent to max growth rate).
b	y-intercept of line tangent to max growth rate.
integral	Area under growth curve.
spar	Smoothing parameter used to generate curve - can be set by passing a `spar` argument to `smooth.spline`.