Adopt PSR-2

[Richtermeister]

In order to maintain an enforceable and consistent coding style amongst collaborators it may be useful to adopt a common standard, such as: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md

Most of the library is already compliant, only changes I see would be:

• individual property/constant declarations
• remove _ from private methods (should be BC, since methods are private)
• add empty line at end of file

Happy to help with implementation if this is acceptable.

[bkuhl]

:+1: Couldn't agree more