vim-patch:8.1.1769: 'shellslash' is also used for completion

Problem:    'shellslash' is also used for completion.
Solution:   Add the 'completeslash' option. (Yasuhiro Matsumoto, closes vim/vim#3612)
ac3150d385

src/nvim/hashtab.h

@@ -51,6 +51,7 @@ typedef struct hashitem_S {
 /// Initial size for a hashtable.
 /// Our items are relatively small and growing is expensive, thus start with 16.
 /// Must be a power of 2.
+/// This allows for storing 10 items (2/3 of 16) before a resize is needed.
 #define HT_INIT_SIZE 16
 
 /// An array-based hashtable.