Reduce size of binary to extent possible

[dkerr64]

Opening this to track and discuss how to reduce the size of the firmware binary. We have maximum available space of (2MB - 64KB) and at times have used over 90% of this... leaving little margin.

The version in PR #26 currently builds at 84.1% but more savings are likely possible. This page documents a number of ESP-IDF config settings that could optimize our build size. We would need to build our own ESP framework as suggested in Issue #13.

Some ideas...

• Remove IPv6 support, we don't use it (at least not for now)
• Reduce TLS cyphers to only those needed for HomeKit
• Remove the virtual filesystem component
• Remove some of the debug/error handling as suggested in above link.

Note: When changing sdkconfig.defaults it is necessary to manually delete the sdkconfig.ratgdo_esp32dev file or the new settings are not picked up.

[dkerr64]

Building with the version of sdkconfig.defaults that is in current repo reduces binary size to 78.1%... and that is without seeking out specific optimizations.