Added ptpb.pw as new and default provider

It's very much like ix.io in feature set, but it also got https
support so it's now the new default provider.

README.org

@@ -20,7 +20,8 @@ easiest way to install and configure packages.
            ("C-c C-p C-r" . webpaste-paste-region)))
 #+END_SRC
 
-** TODO Providers to implement [4/7]
+** TODO Providers to implement [5/8]
+ - [X] ptpb.pw
  - [X] ix.io
  - [X] dpaste.com
  - [X] sprunge.us

webpaste.el

@@ -98,7 +98,17 @@ Usage:
 
 ;;; Define providers
 (defcustom webpaste-providers-alist
-  (list (list "ix.io"
+  (list (list "ptpb.pw"
+              (webpaste-provider
+               :domain "https://ptpb.pw/"
+               :parser 'buffer-string
+               :post-field "c"
+               :success
+               (cl-function (lambda (&key response &allow-other-keys)
+                              (webpaste-return-url
+                               (request-response-header response "Location"))))))
+
+        (list "ix.io"
               (webpaste-provider
                :domain "http://ix.io/"
                :parser 'buffer-string