treewide: automatically md-convert option descriptions

the conversion procedure is simple:

 - find all things that look like options, ie calls to either `mkOption`
   or `lib.mkOption` that take an attrset. remember the attrset as the
   option
 - for all options, find a `description` attribute who's value is not a
   call to `mdDoc` or `lib.mdDoc`
 - textually convert the entire value of the attribute to MD with a few
   simple regexes (the set from mdize-module.sh)
 - if the change produced a change in the manual output, discard
 - if the change kept the manual unchanged, add some text to the
   description to make sure we've actually found an option. if the
   manual changes this time, keep the converted description

this procedure converts 80% of nixos options to markdown. around 2000
options remain to be inspected, but most of those fail the "does not
change the manual output check": currently the MD conversion process
does not faithfully convert docbook tags like <code> and <package>, so
any option using such tags will not be converted at all.

nixos/modules/services/continuous-integration/jenkins/slave.nix

@@ -14,7 +14,7 @@ in {
       enable = mkOption {
         type = types.bool;
         default = false;
-        description = ''
+        description = lib.mdDoc ''
           If true the system will be configured to work as a jenkins slave.
           If the system is also configured to work as a jenkins master then this has no effect.
           In progress: Currently only assures the jenkins user is configured.
@@ -24,7 +24,7 @@ in {
       user = mkOption {
         default = "jenkins";
         type = types.str;
-        description = ''
+        description = lib.mdDoc ''
           User the jenkins slave agent should execute under.
         '';
       };
@@ -32,7 +32,7 @@ in {
       group = mkOption {
         default = "jenkins";
         type = types.str;
-        description = ''
+        description = lib.mdDoc ''
           If the default slave agent user "jenkins" is configured then this is
           the primary group of that user.
         '';
@@ -41,7 +41,7 @@ in {
       home = mkOption {
         default = "/var/lib/jenkins";
         type = types.path;
-        description = ''
+        description = lib.mdDoc ''
           The path to use as JENKINS_HOME. If the default user "jenkins" is configured then
           this is the home of the "jenkins" user.
         '';
@@ -50,7 +50,7 @@ in {
       javaPackage = mkOption {
         default = pkgs.jdk;
         defaultText = literalExpression "pkgs.jdk";
-        description = ''
+        description = lib.mdDoc ''
           Java package to install.
         '';
         type = types.package;