Load/store instructions now supports offset addressing

... and many more:

* Frame Pointer introduced, to ease access to spilled variables on stack
* jump/call labels are now marked with '@' in assembler
* binary is searched for "main" label as a entry point. init state's IP
  is set to it, or default code section base address is used.
* instruction operands are parsed with regular expressions using named
  groups for better readibility
* IO and IRQ handlers have boot- and halt-time callbacks
* basic support for manipulating block of memory larger than 32 bits
* every binary gets its own stack - STACK section is no longer supported
* functions (their labels) are now recorded as symbols
* binary section flags implemented as ctypes bit field
* binary sections can have a name