manpage: reformat lists of subcommands & env vars

Modify parser.rb to add a colon between each term and the line break, which `ronn` converts into a definition list.
The <br> that follows ensures each term description is on a new line in the manpage output, and also replaces the
double trailing space for generating the hard return that follows each term in the HTML output.
Also modify man.rb to print environment variables with list markup matching the cask commands, and then drop
trailing colons from both lists of terms (cask commands, env vars) and non-list terms (analytics, bundle, services;
a <br> is added here because it would prevent the term description from being indented in the manpage output).
https://docs.brew.sh/Manpage#cask-command-options-cask

Library/Homebrew/cask/cmd.rb

@@ -78,7 +78,6 @@ module Cask
 
         Commands:
         #{command_lines.join}
-
         See also: `man brew`
       EOS
     end

Library/Homebrew/cli/parser.rb

@@ -176,7 +176,7 @@ module Homebrew
 
       def usage_banner_text
         @parser.banner
-               .gsub(/^  - (`[^`]+`)\s+/, "\n- \\1  \n  ") # Format `cask` subcommands as MarkDown list.
+               .gsub(/^  - (`[^`]+`)\s+/, "\n- \\1:\n  <br>") # Format `cask` subcommands as Markdown list.
       end
 
       def comma_array(name, description: nil)

Library/Homebrew/dev-cmd/man.rb

@@ -135,6 +135,8 @@ module Homebrew
       when "--markdown"
         ronn_output = ronn_output.gsub(%r{<var>(.*?)</var>}, "*`\\1`*")
                                  .gsub(/\n\n\n+/, "\n\n")
+                                 .gsub(/^(- `[^`]+`):/, "\\1") # drop trailing colons from definition lists
+                                 .gsub(/(?<=\n\n)([\[`].+):\n/, "\\1\n<br>") # replace colons with <br> on subcommands
       when "--roff"
         ronn_output = ronn_output.gsub(%r{<code>(.*?)</code>}, "\\fB\\1\\fR")
                                  .gsub(%r{<var>(.*?)</var>}, "\\fI\\1\\fR")
@@ -234,10 +236,10 @@ module Homebrew
   sig { returns(String) }
   def env_vars_manpage
     lines = Homebrew::EnvConfig::ENVS.flat_map do |env, hash|
-      entry = "  * `#{env}`:\n    #{hash[:description]}\n"
+      entry = "- `#{env}`:\n  <br>#{hash[:description]}\n"
       default = hash[:default_text]
       default ||= "`#{hash[:default]}`." if hash[:default]
-      entry += "\n\n    *Default:* #{default}\n" if default
+      entry += "\n\n  *Default:* #{default}\n" if default
 
       entry
     end