RenyiExtropy 0.4.0

Improved input validation across all functions: each check now produces a distinct, informative error message that names the offending argument.
Added anyNA() guards to all functions accepting probability vectors or matrices, so NA/NaN inputs are caught early.
Added is.matrix() checks to joint_entropy(), conditional_entropy(), and conditional_renyi_extropy().
kl_divergence() and cross_entropy() now emit a warning() (rather than silently replacing) when a zero entry in q is paired with a positive entry in p.
Expanded @examples sections for all exported functions.
Updated DESCRIPTION: added URL and BugReports fields; removed LazyData (no data files shipped).
Comprehensive testthat test suite covering correctness, limit cases, and all input-validation error/warning paths.

RenyiExtropy 0.2.0