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, 1 insertions, 1 deletions

diff --git a/src/nvim/indent_c.c b/src/nvim/indent_c.c
index 6648a9f7c6..d6101357e3 100644
--- a/src/nvim/indent_c.c
+++ b/src/nvim/indent_c.c
@@ -303,7 +303,7 @@ static int cin_isinit(void)
   for (;; ) {
     int i, l;
 
-    for (i = 0; i < (int)(sizeof(skip) / sizeof(char *)); ++i) {
+    for (i = 0; i < (int)ARRAY_SIZE(skip); ++i) {
       l = (int)strlen(skip[i]);
       if (cin_starts_with(s, skip[i])) {
         s = cin_skipcomment(s + l);