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

```
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)
```

- 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

A numeric.

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 $$R = \alpha S \exp(-\beta S)$$

`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`