Support for omitempty, as well as tests for omitempty.

[bbuck]

This pull request will close #73 and add in support for omitempty.

If you want me to clean things up a bit, I can - this works fine but would not be the best structure to add in future "options" to field names.

[bbuck]

I've gone ahead and cleaned this up, turned into something a little more extendable.

I've also taken out the concept that zero numeric values are "empty" and thus would appear in omitempty fields when their values are 0. To compensate, I added omitzero which would omit numeric fields when their values are 0.

type Sample struct {
    User  string `toml:"name"`
    Pass  string `toml:"password,omitempty"`
    Count int    `toml:"count,omitzero"`
}

s := Sample{"username", "", 50}
// Encode =>
// name = "username"
// count = 50
// 

s.Pass = "some password"
s.Count = 0
// Encode =>
// name = "username"
// password = "some password"
//

[BurntSushi]

Looks great! Thank you!

[cespare]

It's unfortunate that omitzero is a separate concept from omitempty. This is an unnecessary break from encoding/json's behavior.

[cespare]

See #120.