Convert everything to c api

include/weaseljson.h

@@ -41,7 +41,8 @@ typedef struct WeaselJsonParser WeaselJsonParser;
 
 /** Create a parser. Increasing stack size increases memory usage but also
  * increases the depth of nested json accepted. `callbacks` and `data` must
- * outlive the returned parser. */
+ * outlive the returned parser. Returns null if there's insufficient available
+ * memory */
 WeaselJsonParser *WeaselJsonParser_create(int stackSize,
                                           const WeaselJsonCallbacks *callbacks,
                                           void *data);
@@ -53,7 +54,8 @@ void WeaselJsonParser_reset(WeaselJsonParser *parser);
 void WeaselJsonParser_destroy(WeaselJsonParser *parser);
 
 /** Incrementally parse `len` more bytes starting at `buf`. `buf` may be
- * modified. Call with `len` 0 to indicate end of data */
+ * modified. Call with `len` 0 to indicate end of data. `buf` may be null if
+ * `len` is 0 */
 WeaselJsonStatus WeaselJsonParser_parse(WeaselJsonParser *parser, char *buf,
                                         int len);