Move coap_pdu_t to coap_pdu_internal.h.
Move internal PDU based function definitions to coap_pdu_internal.h.
Replace most references to "struct coap_pdu_t" with "coap_pdu_t".
Create new enum coap_pdu_type_t, enum coap_pdu_code_t and coap_option_num_t,
using them where appropriate for clarity of documentation.
Provide new functions to allow applications to access/update parts of
coap_pdu_t as appropriate and document as appropriate.
Update examples to use these new access functions where appropriate.
Jon Shallow
e4e067e5fb