Fix various warnings

- unused variable ‘walk’ [-Wunused-variable]
- implicit declaration of built-in function ‘free’
[-Wimplicit-function-declaration]
- initialization discards ‘const’ qualifier from pointer target type
[-Wdiscarded-qualifiers]
- variable 'ram_used' is used uninitialized whenever 'if' condition is
false [-Wsometimes-uninitialized]. This is actually easily reproducible
by specifying `memory_used_method = "XXX"`.
- comparison of integers of different signs: 'int' and 'unsigned long'
[-Wsign-compare] (for `exponent`)

1 files changed, 2 insertions, 2 deletions

diff --git a/include/i3status.h b/include/i3status.h
index e0dff2b..6e5278f 100644
--- a/include/i3status.h
+++ b/include/i3status.h
@@ -206,9 +206,9 @@ char *trim(const char *s);
 /* src/format_placeholders.c */
 typedef struct {
     /* The placeholder to be replaced, e.g., "%title". */
-    char *name;
+    const char *name;
     /* The value this placeholder should be replaced with. */
-    char *value;
+    const char *value;
 } placeholder_t;
 char *format_placeholders(const char *format, placeholder_t *placeholders, int num);