suRtex Beta 0.1

Added stop if data is not a matrix or data frame. Added warning is
level vector lengths differ. Added statlist. Added warning if mean,
median, or sd are used in non-numeric vectors. Statlist is given for
variables in this warning. suRtex now treats all data as factors in
case they are not numeric by default. Added startdoc and enddoc options
for adding extra cat functions when the table is a standalone LaTeX
document. Fixed problem: if no statistics are chosen, table can still
be produced. For mean, median, and standard deviation statistics, all
factor vectors are coerced to numeric.