protobuf-c/TODO

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--- IMPORTANT TODO ---
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- provide example rpc
- proper support for extensions
  - slot for ranges in descriptor
  - extends is implemented as c-style function
    whose name is built from the package, the base message type-name
    and the member.  which takes the base message and returns the
    value, if it is found in "unknown_values".
- implement default values for strings, bytes, and messages.
- ensure enums are int-size
- message__init(...)
       initializes all defaults -- points at static default values
         for strings, bytes and submessages.

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--- NEEDED TESTS ---
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- test:
  - service method lookups
  - out-of-order fields in messages (ie if the number isn't ascending)
  - gaps in numbers: check that the number of ranges is correct
  - default values

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--- DOCUMENTATION ---
---------------------
Document:
  - services
  - default value handling [not implemented yet]
  - check over documentation again

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--- LOW PRIORITY STUFF ---
--------------------------
- support Group (whatever it is)
- almost no code generator options are obeyed

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--- EXTREMELY LOW PRIORITY STUFF ---
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- stop using qsort in the code generator:  find some c++ish way to do it

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--- ISSUES WE ARE PROBABLY GOING TO IGNORE ---
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- strings may not contain NULs

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--- IDEAS TO CONSIDER ---
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- lifetime functions for messages:
   message__new()
       return a new message using an allocator with standard allocation policy
   message__unpack_onto(...)
       unpack onto an initialized message
   message__clear(...)
       clears all allocations, does not free the message itself
   message__free(...)
       free the message.
  [yeah, right: after typing it out, i see it's way too complicated]