rust 1.1.0

New features

plot.ru() can now be used when d > 2: it produces pairwise plots of the
simulated values.
find_lamba(): argument init_lambda added to enable the user to supply an
initial value for the Box-Cox transformation vector lambda.

Unnecessary print statement print(dim(phi)) removed from function
find_lambda().
Unnecessary print statement print(a_algor) removed from function
ru().
Correct lambda$init to lambda$init_psi in ru() when extracting
Box-Cox information.
Documentation of ru() updated to include a description of the returned
function logf_rho() and simulated values sim_vals_rho and to clarify
the meaning of the returned value of f_mode.
ru(): the expression for the inverse Box-Cox transformation in the case
where lambda is exactly 0 has been corrected.
find_lambda(): carry out calculation of the target on a shifted log scale
to avoid underflow.
Set up plot.ru() so that if the user supplies axis labels then they are
used and otherwise the column name(s) of ru_object$sim_vals are used.
Also enable plotmath symbols to be rendered in the axis labels.