Google protobuf support for Lua

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This project offers a simple C library for basic protobuf wire format

encode/decode, it split to three modules:

- pb.decoder: a wire format decode module.

- pb.buffer: a buffer implement that use to encode basic types into

protobuf's wire format.

- pb.conv: a module to convert between integers in protobuf.

Use the C module, one can basicly maintain protobuf data. A test module (WIP)

used to make high level interface to Lua. now it can produce types.lua, a type

describe module generated to help decode protobuf data to Lua table. Now it

can bootstrap itself (i.e. to decode descriptor.pb, and produce types.lua

itself).

this module is still work-in-progress. Some works to do:

- Lua modules handle high level interface to decode/encode protobuf data

from/to Lua table.

- Lua modules to generate pure C module code to enable the ability that

write Lua plugins for protoc on Windows.

protoc need plugins' stdin/stdout works on binary mode. but that's

impossible without modify the Lua code if you use VS compiler and /MT

flag (link with static standard C library).