Refactor Mongoose documentation

PUBLISHED_FROM=e9a4e5c7b4a1d03b93a2a79e29de19e60e919929

docs/c-api/http_server.h/mg_parse_http.md

@@ -0,0 +1,15 @@
+---
+title: "mg_parse_http()"
+decl_name: "mg_parse_http"
+symbol_kind: "func"
+signature: |
+  int mg_parse_http(const char *s, int n, struct http_message *hm, int is_req);
+---
+
+Parses a HTTP message.
+
+`is_req` should be set to 1 if parsing a request, 0 if reply.
+
+Returns the number of bytes parsed. If HTTP message is
+incomplete `0` is returned. On parse error, a negative number is returned. 
+