Convert stock recruit parameters from steepness parameterization to alpha/beta (and vice versa)

## Usage

```
hconv(alpha, phi0, SR = 1, type = 1)
R0conv(alpha, beta, phi0, SR = 1, type = 1)
SRalphaconv(h, phi0, SR = 1, type = 1)
SRbetaconv(h, R0, phi0, SR = 1, type = 1)
```

## Arguments

- alpha
Alpha parameter

- phi0
Unfished spawners per recruit

- SR
Stock-recruit function: (1) Beverton-Holt, or (2) Ricker

- type
The parameterization of the Beverton-Holt function with respect to `alpha`

and `beta`

. See details.

- beta
Beta parameter

- h
Steepness parameter

- R0
Unfished recruitment parameter

## Details

The Type 1 Beverton-Holt equation is
$$R = \alpha S/(1 + \beta S)$$

The Type 2 Beverton-Holt equation is
$$R = S/(\alpha + \beta S)$$

The Ricker equation is
$$R = \alpha S \exp(-\beta S)$$

## Functions

`hconv()`

: Returns steepness (h) from `alpha`

and `phi0`

`R0conv()`

: Returns unfished recruitment (R0) from `alpha`

, `beta`

, and `phi0`

`SRalphaconv()`

: Returns `alpha`

from `h`

and `phi0`

`SRbetaconv()`

: Returns `beta`

from `h`

, `R0`

, and `phi0`