Z80asm: Basic Z80 assembler and linker

Supports:
	- all standard Z80 instructions but any that uses index registers (see Z80asm/instruction_set.txt).
	- labeling, in fact all code must have a label. You must define a _main label as entry point.
	- very few macros, like org, this is not MASM.
	- the only target is obviously the Zilog Z80 family. i8080 code is binary compatible with Z80 but not viceversa.

Assembler and linker are in the same binary and cant be separated in to steps.
The linker outputs a Intel HEX file, you burn it to a EEPROM or load it in a Z80 emulator.

Example program Z80asm/test.asm, test2.asm and test3.asm.

Usage:
	z80asm <assembly file> [-o <output name>]

The assembler will list the assembly, then assemble it, list symbols, link the symbols, list machine code and instructions,
HEX dump the program, and write it to a hex file.