implement custom shorter url support (#28)

Usage: set "--short-api" to "custom", provide url with "--short-url" to shorter
service which returns short link in text form. For paste url mask "{{url}}" must
be used. Link queried with GET request.

Example for Shlink service:
https://doma.in/rest/v2/short-urls/shorten?apiKey=YOURKEY&longUrl={{url}}&format=txt

Signed-off-by: R4SAS <r4sas@i2pmail.org>

pbincli/__init__.py

@@ -2,6 +2,6 @@
 # -*- coding: utf-8 -*-
 
 __author__ = "R4SAS <r4sas@i2pmail.org>"
-__version__ = "0.3.1"
+__version__ = "0.3.2b1"
 __copyright__ = "Copyright (c) R4SAS"
 __license__ = "MIT"