xtrec 1.0.0

• Initial CRAN release.
• Implements the t-REC (iid errors) and t-RREC (robust) panel unit root tests from Westerlund (2015) doi:10.1016/j.jeconom.2014.09.013.
• Supports polynomial trend degrees 0, 1, 2, …
• Asymptotic bias coefficients a_p and b_p computed analytically.
• Panel-level summary statistics for heterogeneity assessment.