context.Bind not support pointer type like *string, *int when request body is form

[cssivision]

context.Bind not support pointer type because mapForm method in binding module not support parse pointer type. if parse pointer type will get response of Unknown type.

whether it is necessary to add support for pointer type? if necessary i will put a pr to add this feature.

it is necessary to my opinion.

[cch123]

#893

[thinkerou]

Implement in #1336 . try it in the latest master branch.