vim: Type search in :MerlinSearch and update the doc

':MerlinSearch' switches between polarity search and search by type
depending on the first character of the query, like is done in the emacs
plugin.

Documentation about the three search functions is added.

vim/merlin/autoload/merlin.vim

@@ -301,6 +301,16 @@ function! merlin#SearchByType(debug,query)
   endif
 endfunction
 
+" Do a polarity search or a search by type depending on the first character of
+" the query.
+function! merlin#Search(debug, query)
+  if a:query =~ "^[-+]"
+    call merlin#PolaritySearch(a:debug, a:query)
+  else
+    call merlin#SearchByType(a:debug, a:query)
+  endif
+endfunction
+
 function! s:StopHighlight()
   if exists('w:enclosing_zone') && w:enclosing_zone != -1
     call matchdelete(w:enclosing_zone)
@@ -821,11 +831,10 @@ function! merlin#Register()
   command! -buffer -nargs=0 MerlinGotoDotMerlin call merlin#GotoDotMerlin()
   command! -buffer -nargs=0 MerlinEchoDotMerlin call merlin#EchoDotMerlin()
 
-  """ Polarity search
-  command! -buffer -complete=customlist,merlin#ExpandTypePrefix -nargs=+ MerlinSearch call merlin#PolaritySearch(0,<q-args>)
-
-  """ Search by type
+  """ Search
+  command! -buffer -complete=customlist,merlin#ExpandTypePrefix -nargs=+ MerlinSearchPolarity call merlin#PolaritySearch(0,<q-args>)
   command! -buffer -complete=customlist,merlin#ExpandTypePrefix -nargs=+ MerlinSearchType call merlin#SearchByType(0,<q-args>)
+  command! -buffer -complete=customlist,merlin#ExpandTypePrefix -nargs=+ MerlinSearch call merlin#Search(0,<q-args>)
 
   """ debug --------------------------------------------------------------------
   command! -buffer -nargs=0 MerlinDebugLastCommands MerlinPy merlin.vim_last_commands()

vim/merlin/doc/merlin.txt

@@ -158,6 +158,44 @@ Act either as *:py* or *:py3* depending on the version of python is used
 by the vim plugin.
 This is only useful if you want to write custom merlin extensions. 
 
+:MerlinSearch                                                  *:MerlinSearch*
+
+Act either as :MerlinSearchPolarity or :MerlinSearchType depending on the first
+character of the query. If the query starts with '-' or '+', then
+:MerlinSearchPolarity is used, otherwise, :MerlinSearchType is used.
+
+>
+  :MerlinSearch -int +string
+  :MerlinSearch int -> string
+<
+
+:MerlinSearchPolarity                                  *:MerlinSearchPolarity*
+
+Search for values in the current scope that have a type matching the query.
+The results are displayed in a completion menu.
+
+The query language is simply a list of path identifiers prefixed by `+` or `-`,
+e.g. `-int`, `-int +string`, `-Hashtbl.t +int`.
+
+`-` is interpreted as "consuming" and `+` as "producing": `-int +string` looks
+for functions consuming an `int` and producing a `string`.
+
+>
+  :MerlinSearchPolarity -int +string
+<
+
+:MerlinSearchType                                          *:MerlinSearchType*
+
+Works similarly to :MerlinSearchPolarity but uses a different query language.
+The results are displayed in a completion menu.
+
+The query language is a list of type constructors separated by '->'.
+Type parameters and functions are allowed: `('a -> bool) -> 'a list -> bool`.
+
+>
+  :MerlinSearchType int -> string
+<
+
 ==============================================================================
 OPTIONS                                                       *merlin-options*