fass: Friendly Assembler

A more human-readable assembler for the 6502 processor.

The spirit of fass is to be as similar as 6502 assembly as possible, but more readable.
In that sense, all fass statements should:

• Be very explicit and obvious about what machine language instruction they produce
• One fass statement equals to exactly one ML instruction (1:1 relationship)
  • A statement that violates this rule has to make it very explicit, E.G. label = A = 1 translates to LDA #1 + STA label to avoid having pairs of load and storage statements everywhere.
• Be deterministic and non ambiguous. Every statement produces always the same output and doesn't depend on anything other than the statement itself.
  • An exception to this rule is that using a label that resolves to a zero page address (0..255) would generate a zero page addressing opcode, while a label referencing higher memory would generate an absolute addressing opcode, and yet that wouldn't be clear by the label's name alone. This could be considered as a silent optimization. Despite that, the user should be able to explicitly force an absolute addressing independently of the reference being in zero page or not.
• Whenever possible, there should be only one way of expressing something.
• Be as obvious and explicit as possible to clearly convey its meaning, but not overly verbose.