Feature: Add handling of absolute path to vimwiki #811 from @justrajdeep

- update vimwiki link handling so that if using env variables it is resolved
- add [[//absolute_path]] to handle absolute path
- updated doc to reflect the changes

test/link_creation.vader

@@ -1,8 +1,68 @@
 Include: vader_includes/vader_setup.vader
 
+# Absolute links {{{1
+####################
+
+Execute (Log):
+  Log 'Absolute links'
+
+# For markdown {{{2
+# ------------------
+
+Execute (Set filename wiki_test.md):
+  Log '>> Absolute link, markdown syntax'
+  file wiki_test.md
+  call SetSyntax('markdown')
+
+Given vimwiki(some wiki link):
+  [test1](//$HOME/in_home1)
+  [test2](//~/in_home2)
+  [test3](///tmp/in_tmp)
+
+Do (Check in_home1):
+  \<Cr>
+  :AssertEqual expand('%'), $HOME.'/in_home1.md'\<Cr>
+
+Do (Check in_home2):
+  j\<Cr>
+  :AssertEqual expand('%'), $HOME.'/in_home2.md'\<Cr>
+
+Do (Check in_tmp):
+  jj\<Cr>
+  :AssertEqual expand('%'), '/tmp/in_tmp.md'\<Cr>
+
+# For Wiki {{{2
+# ------------------
+
+Execute (Set filename wiki_test.wiki):
+  Log '>> Absolute link, wiki syntax'
+  file wiki_test.wiki
+  call SetSyntax('default')
+
+Given vimwiki(some wiki link):
+  [[//$HOME/in_home1]]
+  [[//~/in_home2]]
+  [[///tmp/in_tmp]]
+
+Do (Check in_home1):
+  \<Cr>
+  :AssertEqual expand('%'), $HOME.'/in_home1.wiki'\<Cr>
+
+Do (Check in_home2):
+  j\<Cr>
+  :AssertEqual expand('%'), $HOME.'/in_home2.wiki'\<Cr>
+
+Do (Check in_tmp):
+  jj\<Cr>
+  :AssertEqual expand('%'), '/tmp/in_tmp.wiki'\<Cr>
+
+
 # Link with dot {{{1
 ####################
 
+Execute (Log):
+  Log 'Link  with dot'
+
 Given vimwiki (filnames with dots):
   part1.part2.part3
   part1.part2.part3.md
@@ -39,6 +99,9 @@ Do (j<Cr><Cr>):
 # Rest {{{1
 ##########################
 
+Execute (Log):
+  Log 'And more'
+
 Given vimwiki (Text that is not a wikilink):
   test
   www.google.com