*new proc READ-MESSAGE-BODY: a high-level interface for reading in
message bodies (should be used by all handlers)
*new proc READ-ORDINARY-BODY: reads in message bodies with no transfer
coding applied
*new proc READ-CHUNKED-BODY: reads in message bodies in chunked
transfer coding
*new proc GET-CHUNK-SIZE: reads in and parses the size of the next
chunk in a chunked message body
*helper procs READ-AND-DISCARD-TRAILER and DISCARD-LINE-TERMINATOR
*minor changes to GET-NUMERIC-FIELD-VALUE (cosmetic)
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