Resolves #11, com with any GPIO, CALLR, TRAP implements DOLIT

This snapshot release offers a solution for issue #11

As a preview it also adds the following features:

• Board support
  • Any GPIO or pair of GPIOs from ports PA through PD can be used as an interrupt driven COM port
  • improved interface between 7S-Display core, and board code
• STC user code density
  • relative CALL where possible (2 instead of 3 bytes)
  • pseudo-opcode for DOLIT using TRAP: compiled literals 3 instead of 5 bytes
  • option to disable DOLIT TRAP feature if application doesn't allow 2.5µs added latency

Edit for 49c086f:

• HALT instruction added
• OUT! for board MINDEV fixed

Edit for cadd43f:

• Issue #12 fixed