Add string literals

[FredericDesgreniers]

Add string literals

"some word"

As a valid input for a state.

This would then be converted to a series of input and states for each character.

This means that tokens can be declared as

start {
    "return" => return RETURN
}

Instead of having to manually write the state chaining

[FredericDesgreniers]

Implemented. String literals are stored as char sequences, which are then transformed into a series of intermediate states.