Secure tunneling deadlock fix

• Fixes a potential deadlock when the secure tunneling implementation sends a large payload

Fix memory leaks in connection

What's Changed

• Fix the memory leak in aws-c-io. Update submodule head to the new release. Resolved issue #215

Greengrass IPC Api update

• Adds a new set of Greengrass IPC APIs that return unique_ptr, allowing the operation's scope to be arbitrary and not tied to where the operation was created.

v1.15.1

What's Changed

• Fix bug where DeviceDefender closes stdin. by @graebm in #367
• Fix iOS builds
• Fix crash after failed TLS connection on Unix platforms.

Full Changelog: v1.15.0...v1.15.1

PKCS#11 for mutual TLS

• Support PKCS#11
• Support Windows Server 2008

Secure Tunnel Sample and Submodule Update

• Added a Secure Tunnel Sample
• Updated to latest version of aws-crt-cpp v0.17.9 -> v0.17.10

HTTP Proxy Support for Secure Tunneling

• Added HttpClientConnectionProxyOptions to SecureTunnel
• Added SecureTunnelBuilder

Empty/null payload fixes

• Fixes a crash when using an mqtt will with an empty payload
• Fixes a decoding error when receiving an mqtt message with an empty payload

Multiple crash fixes

• Fix a crash when using eventstream RPC
• Fix a crash in mingw64-based builds for windows

New build flag: USE_CPU_EXTENSION

Build with -DUSE_CPU_EXTENSIONS=OFF to disable CPU-specific functions. This is ON by default.