The traditional linear regression trend, Modified Mann-Kendall (MK)
non-parameter trend and bootstrap trend are included in this package. Linear
regression trend is rewritten by '.lm.fit'. MK trend is rewritten by 'Rcpp'.
Finally, those functions are about 10 times faster than previous version
Hamed, K. H., & Rao, A. R. (1998). A modified Mann-Kendall trend test for
autocorrelated data. Journal of hydrology, 204(1-4), 182-196.