[WIP] Modify the `git logg` alias to show only the newly changed commits from master.

Change the behaviour of `git logg` alias to show the newly changed commits from master branch.
It seems that the limiting the commits can be enabled by specifying:

```
git log master..[branch_name]
```

Also, the current branch name can be obtained by executing: `git symbolic-ref HEAD`.
(Thanks to http://qiita.com/usamik26/items/8aa6c3aed4b9c7dba5ca)
Change the behaviour of `git logg` alias to show only the newly changed commits
Merge pull request #13 from kazu634/20141013_git_logg_modify

[WIP] Modify the `git logg` alias to show only the newly changed commits from master.