added \mjteqn and \mjtdeqn macros (triple-argument versions)
added preview_rd() function
environment variable MATHJAXR_CDN can now be used to specify an alternative URL for a CDN
changed name of environment variable from MATHJAXR.USECDN to MATHJAXR_USECDN
expanded information provided under ‘Issues’
first version released on CRAN
simplified ifelse logic for the \mjeqn and \mjdeqn macros
added \mjseqn and \mjsdeqn macros (single-argument versions)