feat: make configuration options from argtable3.h configurable

Currently several argtable3 options can be modified only by changing
them in source code. This commit makes these options configurable by
adding ifndef guards: ARG_DSTR_SIZE, ARG_CMD_NAME_LEN,
ARG_CMD_DESCRIPTION_LEN.

ARG_DSTR_SIZE option is moved to argtable_private.h for two reasons:

- Having them in argtable_private.h allows defining compiler flags
  (such as -DARG_DSTR_SIZE=100) for argtable3 files only. If the
  definitions are in the public header file (argtable3.h) then
  technically we have to pass -DARG_DSTR_SIZE=100 also to other files
  in the project, so that they evaluate argtable3.h in the same way.
- Having them in argtable3.h is actually not necessary, since they
  are not used anywhere in the public interface.

For the same two reasons, ARG_REPLACE_GETOPT has also been moved into
argtable3_private.h in the same commit.

src/arg_getopt_long.c

@@ -50,6 +50,9 @@
  */
 
 #include "argtable3.h"
+#ifndef ARG_AMALGAMATION
+#include "argtable3_private.h"
+#endif
 
 #if ARG_REPLACE_GETOPT == 1
 

src/argtable3.h

@@ -41,13 +41,16 @@ extern "C" {
 #endif
 
 #define ARG_REX_ICASE 1
-#define ARG_DSTR_SIZE 200
+
+/* Maximum length of the command name */
+#ifndef ARG_CMD_NAME_LEN
 #define ARG_CMD_NAME_LEN 100
-#define ARG_CMD_DESCRIPTION_LEN 256
+#endif /* ARG_CMD_NAME_LEN */
 
-#ifndef ARG_REPLACE_GETOPT
-#define ARG_REPLACE_GETOPT 1 /* use the embedded getopt as the system getopt(3) */
-#endif /* ARG_REPLACE_GETOPT */
+/* Maximum length of the command description */
+#ifndef ARG_CMD_DESCRIPTION_LEN
+#define ARG_CMD_DESCRIPTION_LEN 256
+#endif /* ARG_CMD_DESCRIPTION_LEN */
 
 /* bit masks for arg_hdr.flag */
 enum { ARG_TERMINATOR = 0x1, ARG_HASVALUE = 0x2, ARG_HASOPTVALUE = 0x4 };

src/argtable3_private.h

@@ -43,6 +43,18 @@
 #define ARG_ENABLE_LOG 1
 #endif /* ARG_ENABLE_LOG */
 
+/* Use the embedded getopt as the system getopt(3) */
+#ifndef ARG_REPLACE_GETOPT
+#define ARG_REPLACE_GETOPT 1
+#endif /* ARG_REPLACE_GETOPT */
+
+/* Size of the buffer pre-allocated for dynamic strings.
+ * If the length exceeds this size, the buffer will be dynamically allocated.
+ */
+#ifndef ARG_DSTR_SIZE
+#define ARG_DSTR_SIZE 200
+#endif /* ARG_DSTR_SIZE */
+
 #ifdef __cplusplus
 extern "C" {
 #endif