bcal v1.9 storage expression calculator gets REPL mode

  - evaluate arithmetic expressions involving storage units
  - convert to IEC/SI standard data storage units
  - REPL mode with the last valid result stored for reuse
  - show the address in bytes
  - show address as LBA:OFFSET
  - convert CHS to LBA and vice versa
  - show binary, decimal and hex representation of a number
  - custom sector size, max heads/cylinder and max sectors per track
  - minimal dependencies