Wrapper for selecting different animal movement methods.

This version uses just turn angles and step lengths to define the correlated random walk.

```
move(hypothesis = "crw", ...)
crw(agent, extent, stepLength, stddev, lonlat, torus = FALSE)
# S4 method for SpatialPointsDataFrame
crw(agent, extent, stepLength, stddev, lonlat, torus = FALSE)
# S4 method for SpatialPoints
crw(agent, extent, stepLength, stddev, lonlat, torus = FALSE)
```

## Arguments

- hypothesis
Character vector, length one, indicating which movement
hypothesis/method to test/use. Currently defaults to
'crw' (correlated random walk) using `crw`

.

- ...
arguments passed to the function in `hypothesis`

- agent
A `SpatialPoints*`

object.
If a `SpatialPointsDataFrame`

, 2 of the columns must
be `x1`

and `y1`

, indicating the previous location.
If a `SpatialPoints`

object, then `x1`

and
`y1`

will be assigned randomly.

- extent
An optional `Extent`

object that will be used for `torus`

.

- stepLength
Numeric vector of length 1 or number of agents describing
step length.

- stddev
Numeric vector of length 1 or number of agents describing
standard deviation of wrapped normal turn angles.

- lonlat
Logical. If `TRUE`

, coordinates should be in degrees.
If `FALSE`

coordinates represent planar ('Euclidean')
space (e.g. units of meters)

- torus
Logical. Should the movement be wrapped to the opposite
side of the map, as determined by the `extent`

argument.
Default `FALSE`

.

## Value

A SpatialPointsDataFrame object with updated spatial position defined
by a single occurrence of step length(s) and turn angle(s).

## Details

This simple version of a correlated random walk is largely the version that
was presented in Turchin 1998, but it was also used with bias modifications
in McIntire, Schultz, Crone 2007.

## References

Turchin, P. 1998. Quantitative analysis of movement: measuring and
modeling population redistribution in animals and plants.
Sinauer Associates, Sunderland, MA.

McIntire, E. J. B., C. B. Schultz, and E. E. Crone. 2007.
Designing a network for butterfly habitat restoration: where
individuals, populations and landscapes interact.
Journal of Applied Ecology 44:725-736.