refactor: remove atclient_atsign, atclient_atstr, refactor a bunch of function signatures

[JeremyTubongbanua]

closes #263
closes #247
closes #267
closes #127
closes #145
closes #153
closes #154
closes #128
closes #129
closes #317
closes #341
closes #335
closes #336
closes #172
closes #226
closes #235
closes #346
closes #342

- What I did

Done as of July 12th:

• Refactored atclient_atkey_to_string function signature to take char ** (originally was char *buf, const size_t bufsize, size_t *buflen)
• Refactored atclient_atkey_metadata_to_protocol_str function signature to take char **
• Refactored and optimized atclient_put to reflect changes and added comments to increase readability
• New AES CTR functions. Used to help create an optimal buffer size to be allocated to hold the result of the encrypt/decrypt operation:
• Removed unused function in connection.h/c
• Removed unused function in atkeysfile.h/c

size_t atchops_aes_ctr_ciphertext_size(const size_t plaintextlen);

size_t atchops_aes_ctr_plaintext_size(const size_t ciphertextlen);

Done as of July 16th

• Optimized atclient_delete
• Optimized atclient_put
• Optimized atclient_pkam_authenticate
• Optimized atclient_get_atkeys
• Handle malloc==NULL where it was easy to handle it

Done as of July 18th

• Removed atclient_atstr from atclient_atkey and fixed atclient_atkey unit tests
• Made metadata.h/.c setters from void to return int instead as discussed in at_c: uniformly make all setters return int even if it explicitly returns 0 #317
• Added atclient_atkey_get_type and removed atkeytype from atclient_atkey struct
• Renamed atkey.name to atkey.key

Done as of July 20th

• Finished up metadata.h/.c refactors completely, including some of the to/from jsonstr/cjson node functions
• Removed atstr from metadata
• Made all tests pass
• Removed isHidden (see at_c: remove isHidden from metadata.c and all uses #145 as to why)
• at_c: atkeys.c initializedfields #128 - atkeys.c/.h now has _initializedfields for optimized memory management
• Removed atstr from atkeys
• Removed atstr from atkeysfile
• Deleted atstr and atbytes completely from the code base

Done as of July 22nd

• Removed atclient_atsign
• Cleaned up encryption_key_helpers.h by changing the function signatures to be more predictable
• atclient_delete now returns commit_id

Done as of July 23rd

• notify_params.h/.c (represents notification request object before sending notify command)
• atnotification.h/.c (represents a notification from monitor)

Done as of July 29th

• request_options.c/.h
• atclient_get_shared_key_request_options, atclient_get_public_key_request_options, atclient_get_self_key_request_options implementations
• atclient_delete_request_options
• atclient_put_shared_key_request_options, atclient_put_self_key_request_options, atclient_put_public_key_request_options,
• atclient_put broken down to atclient_put_self_key, _public_key, and _shared_key
• All CRUD operations take the request_options as an optional parameter (NULLABLE)
• atclient_get_self_key takes char ** now
• atclient_get_public_key takes char ** now
• atclient_get_shared_key takes char ** now
• Updated all tests accordingly
• atchops/mbedtls.h
• atclient/mbedtls.h
• atclient/cjson.h
• Removed readonly_src feature from hooks
• port in atclient_connection is now uint16_t

- How to verify it

• Tests still pass

- Description for the changelog