No longer hard limited to <128 byte messages.  Outbound messages are now only
limited by the user's RAM size, (they provide the pointer) rather than by an
internal library buffer.

Receive messages are still limited to the library buffer, but changing the
single #define is now sufficient to change the allowed size.

Headers were updated to provide better code assistance in IDEs.

Work by ReMake Electric, happily returned to the community.

No need to ever use this, so don't keep it around #deffed out.

…removed.

Some methods previously returned 0 for success, (and for failure) and some returned 1 for success and 0 for failure.  Make them all use 0 for success, and different error codes for each failure, and make them proper defines.

This is BACKWARDS INCOMPATIBLE unfortunately :(

Calls that were
   while (client.connect(config.devicename) != 1)
Should now be
   while ((rc = client.connect(config.devicename)) != ERR_OK)

The old code used 1 for success, 0 for failure for:
   connect()
   loop()

The old code used 0 for both success and failure for:
   publish()

The old code used no return code at all for:
   subscribe()

In all cases, the new code returns 0 (ERR_OK) for success, and either
ERR_NOT_CONNECTED or ERR_TIMEOUT_EXCEEDED for the failure cases.  They are now
also broken out per failure code.