Some default mappings can be set to empty strings

This allows the user to not have a mapping. Also, showing a detailed diagnostic
is now possible through a new command.

Fixes #64.

README.md

@@ -415,6 +415,11 @@ A better option would be to use Syntastic which will keep your `locationlist`
 up to date automatically and will also show error/warning notifications in Vim's
 gutter.
 
+### The `YcmShowDetailedDiagnostic` command
+
+This command shows the full diagnostic text when the user's cursor is on the
+line with the diagnostic.
+
 ### The `YcmDebugInfo` command
 
 This will print out various debug information for the current file. Useful to
@@ -579,6 +584,8 @@ default mapping will probably only work in GUI Vim (Gvim or MacVim) and not in
 plain console Vim because the terminal usually does not forward modifier key
 combinations to Vim.
 
+Setting this option to an empty string will make sure no mapping is created.
+
 Default: `<C-Space>`
 
     let g:ycm_key_invoke_completion = '<C-Space>'
@@ -586,7 +593,10 @@ Default: `<C-Space>`
 ### The `g:ycm_key_detailed_diagnostics` option
 
 This option controls the key mapping used to show the full diagnostic text when
-the user's cursor is on the line with the diagnostic.
+the user's cursor is on the line with the diagnostic. It basically calls
+`:YcmShowDetailedDiagnostic`.
+
+Setting this option to an empty string will make sure no mapping is created.
 
 Default: `<leader>d`
 

autoload/youcompleteme.vim

@@ -74,12 +74,16 @@ function! youcompleteme#Enable()
   exe 'inoremap <expr>' . g:ycm_key_previous_completion .
         \ ' pumvisible() ? "\<C-p>" : "\' . g:ycm_key_previous_completion .'"'
 
+  if strlen(g:ycm_key_invoke_completion)
     " <c-x><c-o> trigger omni completion, <c-p> deselects the first completion
     " candidate that vim selects by default
     exe 'inoremap <unique> ' . g:ycm_key_invoke_completion . ' <C-X><C-O><C-P>'
+  endif
 
+  if strlen(g:ycm_key_detailed_diagnostics)
     exe 'nnoremap <unique> ' . g:ycm_key_detailed_diagnostics .
-        \ ' :call <sid>ShowDetailedDiagnostic()<cr>'
+          \ ' :YcmShowDetailedDiagnostic<cr>'
+  endif
 
   py import sys
   py import vim
@@ -404,6 +408,8 @@ function! s:ShowDetailedDiagnostic()
   py ycm_state.ShowDetailedDiagnostic()
 endfunction
 
+command! YcmShowDetailedDiagnostic call s:ShowDetailedDiagnostic()
+
 
 " This is what Syntastic calls indirectly when it decides an auto-check is
 " required (currently that's on buffer save) OR when the SyntasticCheck command