Update net/rabbitmq-c to 0.7.0.

- Tools: Add support for heartbeats
- CI: Add continuous integration on Win32 using Appveyor
- Tests: only link against static libraries
- Lib: add support for EXTERNAL SASL method
- Lib: fix incorrect parameters to WSAPoll on Win32
- Lib: use non-blocking sockets internally
- Lib: simplify timer/timeout logic
- Lib: add support for heartbeat checks in blocking send calls
- Lib: Fix warnings on Win32
- Lib: Add support for RabbitMQ auth failure extension
- Lib: allow calling functions to override client-properties
- examples: replace usleep() with nanosleep()
- Lib: add AMQP_VERSION code
- Lib: fix res maybe returned uninitialized in amqp_merge_capbilities
- Lib: Fix SSL_connection status check
- Lib: Fix issues with c89 compatiblity
- Lib: perf improvements when sending small messages by hinting
  to the OS message boundaries.
- Lib: add select()-based timeout implementation
- CI: add ubsan, asan, and tsan CI builds

(fhajny)