feat: -file param support regular path

[ShuaiGao]

In my project, a also need to gen code with this tool. i want to use regular path match files.

by this change, can use tool by command:

gomodifytags -file "pkg/gen/api/*pb.go" -all -add-tags form -w -quiet -skip-unexported

[ShuaiGao]

is ok by the command:

gomodifytags -all -add-tags form -w -quiet -skip-unexported  -file pkg/gen/api/*pb.go

[ShuaiGao]

I might be right，then i reopened it. Can someone help me?

[anurag925]

@ShuaiGao #110 i also added a similar feature with less intrusion.
Basically this will generate for an entire dir if all are go files else it will throw error.

not just go files but any file written in go formate
i can add a pattern to filter files but i dont thik that is going to be use case for many