Fine-grained memory operation with dcurl_entry

[ajblane]

For example of using dcurl API,

int8_t  *ret_trytes = null;
ret_trytes = dcurl_entry(...);
dcurl_destroy();

The ret_trytes is required to manually use free(), for example:

int8_t  *ret_trytes = null;
ret_trytes = dcurl_entry(...);
dcurl_destroy();
free(ret_trytes);

I suggest the dcurl_destroy() API can be added a argument to release ret_trytes, for example:

int8_t  *ret_trytes = null;
ret_trytes = dcurl_entry(...);
dcurl_destroy(ret_trytes);

This is because the sematic of dcurl_destroy is destroying usage resources. For using dcurl API, a developer maybe imagine ret_trytes can be released without using free() after using dcurl_destroy(). Would this suggestion is better?

[jserv]

The call sequence should be dcurl_init -> dcurl_entry -> dcurl_destroy where dcurl_init and dcurl_destroy are of the pair. I would suggest to add new function named dcurl_release which releases the resources allocated by dcurl_entry.

[furuame]

It seems that dcurl_release do the same thing as free, but more readable.
If ret_trytes passed as an argument, we can avoid this problem and the length of return tryte is known at static time.

int8_t ret_trytes[RETURN_TRYTES_LENGTH];
dcurl_entry(ret_trytes, ...);

[jserv]

Related: #20
Cc. @chenwei-tw

[ajblane]

The PR #59 achieves the goal. Close.