demand 1.0.0

Adds a top level demand(variable) method to return a variable if it's present and optionally of the right type. Otherwise, a default or nil is returned. demand() replaces long lines of repetitive code to check for nil?/present?/empty?, etc., hard-to-read ternary operators (?:) and if statements. A block can also be specified, which only runs (with the variable) if the checks pass.