Improve shr/eww handling of mailto URLs
* lisp/net/eww.el (eww): Use function-put in place of put, as recommended in "(elisp) Symbol Plists". (eww-follow-link): * lisp/net/shr.el (shr-browse-url): Rather than call browse-url-mail directly, call browse-url which respects the user options browse-url-handlers and browse-url-mailto-function. (Bug#41133) (shr--current-link-region): Return nil if there is no link at point. (shr--blink-link): Adapt accordingly. (shr-fill-line, shr-indent, shr-table-body): Refactor to avoid some unnecessary allocations. * etc/NEWS: Announce that eww-follow-link and shr-browse-url support custom URL handlers.