add full MIT license text

Hi Ilya,

Thank you very much for your work on em-socksify. @niteshnarayanlal is working on packaging this gem for Fedora (https://bugzilla.redhat.com/1063040), and the Fedora Packaging Guidelines suggest that we ask you to include a LICENSE file in the root of the project. By including a copy of the exact MIT license text, you will make the terms of the em-socksify license very clear.

Also, in the specific case of em-socksify's MIT license, all derivative copies of em-socksify are required to contain the disclaimer text within the MIT license (as described in the sentence "The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.") So in order to ease development and distribution of em-socksify, it makes sense to simply include this text in the upstream project.

More details about this can be found on Fedora's wiki, under the "License Text" section: https://fedoraproject.org/wiki/Packaging:LicensingGuidelines#License_Text

Would you mind adding this LICENSE file with the MIT license text to the git repo and the gem?