Construct a marked space-time planar point pattern from a
list object
Usage
## S3 method for class 'list':
mstppp(P, ...)
Arguments
P
list object containing $xyt, an (n x 3) matrix
corresponding to (x,y,t) values; $tlim, a vector of
length 2 givign the observation time window, $window
giving an owin spatial observation winow, see ?owin for
more details, and $data, a data frame c