Improve warn or deprecated message in v1 code (#429)

Resolve #353


TODOs
- [x] add `warn ...` for all functions & check if destination is correct
- I used
https://gist.github.com/Yang-33/833011e6adcced62bf893e44cdeb9993 to
check this. destination is checked by my eye..
- [x] add `@deprecated ....` with message for all functions
- I used
https://gist.github.com/Yang-33/341547bbd031ce22152163077636edc6 to
insert comment, though script itself is a little bit wrong. I fixed
comment in client.rb after running the script.
- [x] add `@deprecated ....` for all classes

Author: Yang-33

lib/line/bot/v1/api.rb

@@ -16,6 +16,8 @@
 
 module Line
   module Bot
+    # @deprecated
+    # This is obsolete.
     module API
       DEFAULT_OAUTH_ENDPOINT = "https://api.line.me"
       DEFAULT_ENDPOINT = "https://api.line.me/v2"

lib/line/bot/v1/api/errors.rb

@@ -15,6 +15,8 @@
 module Line
   module Bot
     module API
+      # @deprecated
+      # This is obsolete. (and there is no caller...)
       class Error < StandardError; end
     end
   end

lib/line/bot/v1/api/version.rb

@@ -15,6 +15,8 @@
 module Line
   module Bot
     module API
+      # @deprecated
+      # Use {Line::Bot::V2::VERSION} instead.
       VERSION = "1.29.0"
     end
   end