Generalize `dimensions` into a `multiple` input type

[davidomarf]

So far, ginpar has only one custom input type: dimensions. This creates two inputs in a single form row separated with a 'x'.

However, there are several more inputs that could use a generalized pattern: multi.

• Specify the main name for multi.
• Specify the number of values the input will take.
• Specify the type of all the values, or each value.

This should create a single <label id="{{name}}"> tag, with as many inputs were specified, each one with its own type and default values. Its id should be {{name + "-i"}}, with a different i for each input.

This could be used to generate better range inputs with number type instead of plain range type.