Support for PHP 7

[janbarasek]

Solve #732

• Added support for PHP 7
• Used all new PHP 7 features
• Strict types
• declare(strict_types=1);
• Input and return data types in methods
• Whole code refactoring and fix better readable
• Refactoring to tab and PSR-4 convention
• Add public method visibility

This pull request and change is maximally back compatible, but I renamed all variable names and keep different property name convention.

Please let me know which changes are acceptable to you, because I think this package should keep progress.

[GrahamCampbell]

How much slower is this code than the original (on the same PHP version)?

[janbarasek]

@GrahamCampbell Sorry for late answer, but I must make some performance testing.

Speed is same +/- 5 %, my suggestion does not change speed.