REORG: http: move error codes production and processing to http.c

These error codes and messages are agnostic to the version, even if
they are represented as HTTP/1.0 messages. Ultimately they will have
to be transformed into internal HTTP messages to be used everywhere.

The HTTP/1.1 100 Continue message was turned to an IST and the local
copy in the Lua code was removed.
diff --git a/include/common/http.h b/include/common/http.h
index 4184a47..90d914a 100644
--- a/include/common/http.h
+++ b/include/common/http.h
@@ -110,10 +110,20 @@
 extern struct buffer http_err_chunks[HTTP_ERR_SIZE];
 const struct ist http_known_methods[HTTP_METH_OTHER];
 extern const uint8_t http_char_classes[256];
+
+const struct ist HTTP_100;
+extern const char *HTTP_301;
 extern const char *HTTP_302;
 extern const char *HTTP_303;
+extern const char *HTTP_307;
+extern const char *HTTP_308;
+extern const char *HTTP_401_fmt;
+extern const char *HTTP_407_fmt;
 
+int init_http(char **err);
 enum http_meth_t find_http_meth(const char *str, const int len);
+const int http_get_status_idx(unsigned int status);
+const char *http_get_reason(unsigned int status);
 struct ist http_get_path(const struct ist uri);
 
 #endif /* _COMMON_HTTP_H */