Create C SDK HIP-323

[gregscullard]

HIP-323 proposes a new C SDK, this discussion is open to comment on the HIP (#323)

[mohsin-hedera]

@gregscullard shall we add that SDK is to maintain feature parity with other under-development HIPs, e.g retry mechanism, file append/contract upload, wallet-provider interface.

[gregscullard]

Added to the HIP under "Specifications"

• The C SDK must have feature-parity with other SDKs and include HIPs that are under development or to be approved