Moved from spine cased to camel cased

The nodes, variables and children now use camel cased ids instead of
spinal cased because it's what modern file formats use in general. Even
for XML it's recommended to my surprise.

Bugfix for object accessor setters

When supplying null, it resulted in an error

Object accessor data type bugfix

Created a helper for boolean variables

Fixed a bug for validating object variables during decoding

Merge pull request #1 from harm-less/improved-variables

Improved variables and child functionalities

Moved a dependency to non-dev require

Updated the readme

Updated the readme with all the info people might need in the beginning

Updated composer.json

I made sure it's ready for the first release on Composer

Full coverage for EncoderNodeChild.php