1.0.4 development updates

Over on my side, I released fork versions for my own use: 1.0.2 and 1.0.3. 

I hope to merge 1.0.4 into the main repository. These are the changelog:

- removed vendor from repository
- added Travis CI config
- updated PHPUnit config
- PSR-2 compliance update
- updated dependency stability in composer to Stable (instead of dev)
- removed static properties and methods in Captcha, as singleton has already been used (for testability)
- added improved random string generator, removed characters that can cause homoglyphs
- added 3 more backgrounds
- added new font: FreckleFace with license
- replaced `rand()` with either `mt_rand()` or `array_rand()`
- updated default configurations
  - 6 characters instead of 5
  - spacing between characters are randomized (from config selection)
- improved validation loading, plus added default error message for `captcha`
- added Response making (as proposed by @splinter89 but slightly different)
- added documentation to config
- used `Config::get('app.key')` in the hash process (app-specific hashes)
- Forget sessionhash on check to prevent replay attacks