nostrdb/Inital embedded content parser

This adds some initial code for nostrdb content parsing.

We still need to write tests for encoding and decoding, so this is
likely not working yet.

Signed-off-by: William Casarin <jb55@jb55.com>

nostrdb/src/bolt11/bech32.h

@@ -123,7 +123,8 @@ bech32_encoding bech32_decode_len(
     uint8_t *data,
     size_t *data_len,
     const char *input,
-    size_t input_len
+    size_t input_len,
+    int max_prefix_len
 );
 
 /* Helper from bech32: translates inbits-bit bytes to outbits-bit bytes.