RFC: Gina commit behavior

[lambdalisue]

Currently, the behavior of :Gina commit is

1. When user close a gina-commit buffer with :wq, the commit message will be committed without prompt
2. When user close a gina-commit buffer with :q, a prompt will be appeared then
   1. When user hit <Enter> or type Y(es), the commit message will be committed
   2. When user type N(o), the commit message will NOT be committed and the message will be cached so that if user re-open a gina-commit buffer, the cached message is used as a default message

However, as @bimlas mentioned in #44, gina.vim currently get a cached commit message by

1. Perform an actual commit with cached message
2. Get a cleaned up commit message
3. Reset a previous commit
4. Remove reflogs for above operations

To get a correct cleaned up commit message.

As you notice, this is a bit hackie code and may have some problems. Additionally I noticed that the priority of caching is not really high and I seldom use this feature.
So now I'm thinking about dropping this cache mechanisms to simplify as like #44.
Once I simplify as #44 (or simply merge #44), the behavior would become

1. When user close a gina-commit buffer with :wq, the commit message will be committed without prompt
2. When user close a gina-commit buffer with :q, a prompt will be appeared then
   1. When user hit <Enter> or type Y(es), the commit message will be committed
   2. When user type N(o), the commit message will NOT be committed and the message will be discarded and when user re-open a gina-commit buffer, an empty commit message will be used (This is a different behavior)

While this change a behavior, I would like to hear your opinions before I did. This behavior should be settled before the first production release (better to settle before the third beta release).

It related to #59 a bit as well.

[SevereOverfl0w]

Is there a reason to prompt Yes/No on :q? Particularly if the buffer is not modified?

I'm wondering how common it is to accidentally do :q when you meant :wq

[lambdalisue]

Because sometime I would NOT like to commit.

[SevereOverfl0w]

Ah, I understand now. I hadn't considered that you might do: :w followed by :q.

I think the feature I'd like adding is that if the commit is empty when I do :q, then "No" is the default. Similar to fugitive.

[bimlas]

Opened #94 for :q behaviour.

[lambdalisue]

I haven't face any issue on the current implementation so I decided to not simplify