[expand] adding improvements to root expansions (using possible phrase roots even if they're abbreviated e.g. "E Ctr St", adding special valid components check for root expansions beyond what's stored in the build address dictionaries), removing spaces before checking unique strings, only splitting numeric from alpha in the case of non-ordinals, using cstring_array internally and char ** in the public API

src/tokens.h

@@ -14,6 +14,8 @@
 
 typedef libpostal_token_t token_t;
 
+#define NULL_TOKEN (token_t){0, 0, END}
+
 VECTOR_INIT(token_array, token_t)
 
 typedef struct tokenized_string {