[build] adding libpostal_setup_datadir, libpostal_setup_parser_datadir, libpostal_setup_language_classifier_datadir functions for configuring the datadir at runtime

src/file_utils.c

@@ -36,6 +36,21 @@ bool is_relative_path(struct dirent *ent) {
     return strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0;
 }
 
+char *path_vjoin(int n, va_list args) {
+    char_array *path = char_array_new();
+    if (path == NULL) return NULL;
+    char_array_add_vjoined(path, PATH_SEPARATOR, true, n, args);
+    return char_array_to_string(path);
+}
+
+char *path_join(int n, ...) {
+    va_list args;
+    va_start(args, n);
+    char *path = path_vjoin(n, args);
+    va_end(args);
+    return path;
+}
+
 inline uint64_t file_deserialize_uint64(unsigned char *buf) {
     return ((uint64_t)buf[0] << 56) | 
            ((uint64_t)buf[1] << 48) |