http_header_clean() function

The header

Add a key-value pair of http header to the list, note that with value = NULL, this function will remove the header with `key` already exists in the list.

Cleanup with http_header_clean and destroy http header handle object

Remove the header with key from the headers list

Sample as `http_header_set` but the value can be formated

Get a value of header in header list The address of the value will be assign set to `value` parameter or NULL if no header with the key exists in the list

Create HTTP header string from the header with index, output string to buffer with buffer_len Also return the last index of header was generated