Define and use the ARRAY_SIZE macro

A similar macro is defined in the Linux kernel [1].

To refactor the code I used a slightly modified Coccinelle script I found in
[2].

```diff
// Use the macro ARRAY_SIZE when possible
//
// Confidence: High
// Copyright: (C) Gilles Muller, Julia Lawall, EMN, DIKU.  GPLv2.
// URL: http://www.emn.fr/x-info/coccinelle/rules/array.html
// Options: -I ... -all_includes can give more complete results

@@
type T;
T[] E;
@@

- (sizeof(E)/sizeof(*E))
+ ARRAY_SIZE(E)

@@
type T;
T[] E;
@@

- (sizeof(E)/sizeof(E[...]))
+ ARRAY_SIZE(E)

@@
type T;
T[] E;
@@

- (sizeof(E)/sizeof(T))
+ ARRAY_SIZE(E)

@n@
identifier AS,E;
@@

- #define AS(E) ARRAY_SIZE(E)

@@
expression E;
identifier n.AS;
@@

- AS(E)
+ ARRAY_SIZE(E)
```

`spatch --in-place --sp-file array_size.cocci -I src/ -I build/include/ -I build/src/nvim/auto/ src/nvim/*.c`

[1] http://lxr.free-electrons.com/source/include/linux/kernel.h#L54
[2] http://www.emn.fr/z-info/coccinelle/rules/#macros

1 files changed, 4 insertions, 4 deletions

diff --git a/src/nvim/option.c b/src/nvim/option.c
index 2b3c87511e..fe2c756c01 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -1883,7 +1883,7 @@ void set_init_1(void)
     int mustfree;
 
     ga_init(&ga, 1, 100);
-    for (n = 0; n < (long)(sizeof(names) / sizeof(char *)); ++n) {
+    for (n = 0; n < (long)ARRAY_SIZE(names); ++n) {
       mustfree = FALSE;
 # ifdef UNIX
       if (*names[n] == NUL)
@@ -4723,10 +4723,10 @@ static char_u *set_chars_option(char_u **varp)
 
   if (varp == &p_lcs) {
     tab = lcstab;
-    entries = sizeof(lcstab) / sizeof(struct charstab);
+    entries = ARRAY_SIZE(lcstab);
   } else {
     tab = filltab;
-    entries = sizeof(filltab) / sizeof(struct charstab);
+    entries = ARRAY_SIZE(filltab);
   }
 
   /* first round: check for valid value, second round: assign values */
@@ -7250,7 +7250,7 @@ int ExpandSettings(expand_T *xp, regmatch_T *regmatch, int *num_file, char_u ***
   for (loop = 0; loop <= 1; ++loop) {
     regmatch->rm_ic = ic;
     if (xp->xp_context != EXPAND_BOOL_SETTINGS) {
-      for (match = 0; match < (int)(sizeof(names) / sizeof(char *));
+      for (match = 0; match < (int)ARRAY_SIZE(names);
            ++match)
         if (vim_regexec(regmatch, (char_u *)names[match], (colnr_T)0)) {
           if (loop == 0)