Pull Request: Add rakefile

@brettweavnet @thbishop here is the first stab at automating the tagging of a branch.

it can be run by doing a `rake tag_master`

Here is a sample of two runs, once is successful the other one tries to tag something when the tag already exists. Can we rely on the built in fatal or do we have to specifically try and capture that.

```
$ rake tag_master
Already on 'master'
Will tag master branch with sha: eb3257ef0c95f441d264173e633b955d09ae2993
 to tag version: 0.1.6
Counting objects: 1, done.
Writing objects: 100% (1/1), 163 bytes, done.
Total 1 (delta 0), reused 0 (delta 0)
To git@github.com:keviny22/rspec_dev.git
 * [new tag]         0.1.6 -> 0.1.6
```
```
$ rake tag_master
Already on 'master'
Will tag master branch with sha: eb3257ef0c95f441d264173e633b955d09ae2993
 to tag version: 0.1.6
fatal: tag '0.1.6' already exists
Everything up-to-date

```