Mark some constant data as const.

Issue #95.

src/dump.c

@@ -38,7 +38,7 @@ static int dump_to_file(const char *buffer, size_t size, void *data)
 }
 
 /* 32 spaces (the maximum indentation size) */
-static char whitespace[] = "                                ";
+static const char whitespace[] = "                                ";
 
 static int dump_indent(size_t flags, int depth, int space, json_dump_callback_t dump, void *data)
 {

src/hashtable.c

@@ -74,7 +74,7 @@ static void insert_to_bucket(hashtable_t *hashtable, bucket_t *bucket,
     }
 }
 
-static size_t primes[] = {
+static const size_t primes[] = {
     5, 13, 23, 53, 97, 193, 389, 769, 1543, 3079, 6151, 12289, 24593,
     49157, 98317, 196613, 393241, 786433, 1572869, 3145739, 6291469,
     12582917, 25165843, 50331653, 100663319, 201326611, 402653189,

src/pack_unpack.c

@@ -21,7 +21,7 @@ typedef struct {
     int column;
 } scanner_t;
 
-static const char *type_names[] = {
+static const char * const type_names[] = {
     "object",
     "array",
     "string",
@@ -34,7 +34,7 @@ static const char *type_names[] = {
 
 #define type_name(x) type_names[json_typeof(x)]
 
-static const char *unpack_value_starters = "{[siIbfFOon";
+static const char * const unpack_value_starters = "{[siIbfFOon";
 
 
 static void scanner_init(scanner_t *s, json_error_t *error,