add support to report size of compiled sketch

[ianfixes]

https://arduino.stackexchange.com/questions/8058/how-can-arduino-source-code-be-tested-automatically-continuous-integration

[ianfixes]

This can be found in the ret[:out] of ArduinoCmd.verify_sketch:

Sketch uses 22084 bytes (4%) of program storage space. Maximum is 524288 bytes.

To handle multiple locales, will probably need to parse this with a regex like

/^[^\d]+ (\d+) [^\(]+\((\d{1,3})%\) /