Type-field documentation only shows up with the type itself is also documented

[mauro3]

Consider:

               _                                                                                                                                                         
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.7.0-DEV.5095 (2018-05-12 22:13 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit 2a21849b10* (0 days old master)
|__/                   |  x86_64-pc-linux-gnu

julia> struct A
       "a"
       a
       end                                                                                                                                                               
                                                                                                                                                                         
help?> A.a                                                                                                                                                               
  A has fields a.                                                                                                                                                        
                                                                                                                                                                         

julia> "A" 
       struct A
       "a"
       a
       end                                                                                                                                                               
A                                                                                                                                                                        

help?> A.a # now the "a"-docs is retrieved:
  a

Not really important... Maybe best would be to throw an error in the first case.

Please add the docsystem label.