Fix badly encoded subject in mailto templates
user
```ruby
# From https://stackoverflow.com/questions/15976495/how-to-url-encode-in-jekyll-liquid/17769287#17769287
require 'liquid'
require 'uri'

# Percent encoding for URI conforming to RFC 3986.
# Ref: http://tools.ietf.org/html/rfc3986#page-12
module URLEncoding
  def url_encode(url)
    return URI.escape(url, Regexp.new("[^#{URI::PATTERN::UNRESERVED}]"))
  end
end

Liquid::Template.register_filter(URLEncoding)
```
assistant