Configure FDB_API_VERSION dynamically

[kocolosk]

This patch set dynamically detects the maximum API version supported by the installed FDB client library and builds the NIF wrapper against that version automatically.

Older API versions can still be selected at runtime as usual through the application environment; this just ensures we have the largest possible range at our disposal, without restricting the versions of the client library we can support with a single branch of this codebase.

Closes #34 Closes #38

[kocolosk]

While we are technically green on 6.3 here, it seems there are a handful of changes in API version 630 that we ought to be accounting for:

https://apple.github.io/foundationdb/api-version-upgrade-guide.html#api-version-630

Specifically:

• The get_addresses_for_key function now returns strings that include the port in the address. Prior to API version 630, this required using the INCLUDE_PORT_IN_ADDRESS option, which has now been deprecated.
• The ENABLE_SLOW_TASK_PROFILING network option has been replaced by ENABLE_RUN_LOOP_PROFILING and is now deprecated.
• The FDBKeyValue struct’s key and value members have changed type from void* to uint8_t*.

[kocolosk]

Will squash the CI commits into one to clean up the history, but this is stacked on top of #33 so I think I may wait until that one is merged to proceed further.