Update changelog and sphix config to use extlinks

Signed-off-by: Hiroshi Miura <miurahr@linux.com>

docs/conf.py

@@ -31,6 +31,7 @@ import os
 extensions = [
     'sphinx.ext.autodoc',
     'sphinx.ext.coverage',
+    'sphinx.ext.extlinks',
 ]
 
 # Add any paths that contain templates here, relative to this directory.
@@ -57,9 +58,9 @@ author = u'Hiroshi Miura'
 # built documents.
 #
 # The short X.Y version.
-version = u'0.3'
+version = u'0.5'
 # The full version, including alpha/beta/rc tags.
-release = u'0.3.1'
+release = u'0.5b2'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
@@ -284,3 +285,10 @@ texinfo_documents = [
 
 # If true, do not generate a @detailmenu in the "Top" node's menu.
 #texinfo_no_detailmenu = False
+
+#-- Options for extlink extension
+extlinks = {'issue': ('https://github.com/miurahr/aqtinstall/issues/%s',
+                      'issue ')}
+
+#-- Options for linkcheck
+linkcheck_ignore = [r'https://github.com/miurahr/aqtinstall/compare/.+']