Working roman numerals simple representation and convertion

First basic (hopefully) working part of the project, but still not
completly tested. Roman numerals can be stored if they have a correct
syntax, a convertion arabic <-> roman is possible and roman numerals
can be stored paired with their value. Test classes are also given for
every class, but not all of them are completely written.

Changelog:

 - RomanNumeral stores roman numerals (duh) with the correct syntax only

 - Converter performs a convertion from roman to arabic and vice-versa.
   Stores the values of the roman digits

 - RomanChar is a simple pair stucture used in Converter

 - RomanInteger stores the pair RomanNumeral with its arabic value (an
   Integer) and updates the value of both when one is updates. This
   means any change in the arabic value modifies the roman string and
   vice-versa
Add Mozilla Public License v2.0

FAQ about the MPL: https://www.mozilla.org/MPL/2.0/FAQ.html

Short explanation: the copyleft applies to any files containing MPLed code. You are free to use the software for your private usage and redistribute the software without modifications. You are free to modify the software but you should always provide the source files of your modifications and release them with the MPL. If you use the software (modified or not) in any larger project, including proprietary software, just the originally MPL sources have to be redistributed as that, if modified.
Merging licence from master to develop

After adding the Mozilla Public Licence file in LICENSE.md on github.com (because of their automatic tool) I'm copying it into develop.