Some struct fields are not go-idiomatic

[philcluff]

Hi there,

Some field names in the structs in structure.go are not go-idiomatic, for example:

ProgramId (ProgramID)
GroupId (GroupID)
SeqId (SeqID)
Iframe (IFrame)

Happy to provide a PR if you want to go in this direction.

Cheers,

[grafov]

Well, historically development of the project was not strongly follow go-idioms and make API follow rules of naming is good idea. But the library already used in some proprietary software and these changes will made it incompatible. Anyway I plan to cleanup code in this direction before 1.0 but not in near release. Now I interested in bugfixes and supporting of latest M3U8 specs.

I left this issue open for discussion for the library users.