Tcl/Tk 9.1 adds accessibility, Unicode and timer commands

Tcl/Tk 9.1 adds screen-reader support, initial bidirectional text and right-to-left language support, and the 'ttk::toggleswitch' widget in Tk.

Tcl gains Unicode normalization through a new unicode command and C APIs, plus a monotonic timer command with microsecond resolution. The release also introduces list filtering, child-interpreter variable access, new subst and switch options, and platform-specific filesystem and executable-search revisions.