📚️ Fix ghost method: directives broken by rdoc 8.0

rdoc v8.0 silently dropped support for using the `method:` directive
without a leading colon.

As it turns out, I used the `method:` directive a _lot_.

See ruby/rdoc#1760.

Author: nevans

lib/net/imap/config.rb

@@ -196,7 +196,7 @@ def self.[](config)
       # #load_defaults will not override #debug.
       attr_accessor :debug, type: :boolean, default: false
 
-      # method: debug?
+      # :method: debug?
       # :call-seq: debug? -> boolean
       #
       # Alias for #debug

lib/net/imap/esearch_result.rb

@@ -193,11 +193,11 @@ def initialize(range:, results:)
         end
 
         ##
-        # method: range
+        # :method: range
         # :call-seq: range -> range
 
         ##
-        # method: results
+        # :method: results
         # :call-seq: results -> sequence set or nil
 
         # Converts #results to an array of integers.

lib/net/imap/fetch_data.rb

@@ -104,7 +104,7 @@ class IMAP < Protocol
     #
     class FetchStruct < Struct
       ##
-      # method: attr
+      # :method: attr
       # :call-seq: attr -> hash
       #
       # Each key specifies a message attribute, and the value is the
@@ -518,7 +518,7 @@ def section_attr(attr, part = [], text = nil, offset: nil)
     # See FetchStruct documentation for a list of standard message attributes.
     class FetchData < FetchStruct.new(:seqno, :attr)
       ##
-      # method: seqno
+      # :method: seqno
       # :call-seq: seqno -> Integer
       #
       # The message sequence number.
@@ -532,7 +532,7 @@ class FetchData < FetchStruct.new(:seqno, :attr)
       #   UIDFetchData will raise a NoMethodError.
 
       ##
-      # method: attr
+      # :method: attr
       # :call-seq: attr -> hash
       #
       # Each key specifies a message attribute, and the value is the
@@ -558,7 +558,7 @@ class FetchData < FetchStruct.new(:seqno, :attr)
     # See FetchStruct documentation for a list of standard message attributes.
     class UIDFetchData < FetchStruct.new(:uid, :attr)
       ##
-      # method: uid
+      # :method: uid
       # call-seq: uid -> Integer
       #
       # A number expressing the unique identifier of the message.
@@ -568,7 +568,7 @@ class UIDFetchData < FetchStruct.new(:uid, :attr)
       #   returns the uniqueid at the beginning of the +UIDFETCH+ response.
 
       ##
-      # method: attr
+      # :method: attr
       # call-seq: attr -> hash
       #
       # Each key specifies a message attribute, and the value is the