Preset variables

Charcoal has a few variables set to a certain value by default.

Variable	Value
θ	First input.
η	Second input.
ζ	Third input.
ε	Fourth input.
δ	Fifth input.
γ	Lowercase letters from a to z.
β	Uppercase letters from A to Z.
α	The empty string.
ω	10.
ψ	1000.