www/nsm: Update to 1.21

Changelog picked from https://github.com/nifty-site-manager/nsm/releases:

Nift (aka nsm) v1.21
Release Notes:
    removed trailing '/' or '\' from @contentdir and @sitedir output
    fixed bugs with @contentdir, @sitedir, @contentext syntax
    fixed indenting when parsing parameters
    added more error handling with Nift commands new-[cont/page]-ext
    added file input syntax @RawContent, @inputraw, @scriptraw, @systemraw to template language
    added user input syntax @userin, @userfilein to template language

(ng0)