ASCII syntax for phi expressions

[yegor256]

Let's allow ASCII in phi expressions, on top of UTF:

⟦    = [[
⟧    = ]]
Δ⤍   = D>
λ⤍   = L>
↦    = ->
∅    = ?
φ    = @
ξ    = $
⊥    = T
Φ    = Q
Φ̇    = QQ
ρ    = ^

Let's add all of them to all-the-basics.phi.

[maxonfjvipon]

@yegor256 what about α?

[yegor256]

@maxonfjvipon maybe this way:

α0 ↦ e     = 0> e
α1 ↦ e     = 1> e
α2 ↦ e     = 2> e
etc.