PEG parser-generator for PHP

This is a somehow opinionated continuation of combyna/php-peg, which was "a minimally invasive fork" of the original hafriedlander/php-peg.

From the several originally available types of PEG parsers only Basic and Packrat (recommended) remain now.

Notable features of this fork:

Fix, Optimization: Packrat parser overhaul. Simplified logic using arrays instead of a string. Arrays ultimately seemed to be more fit for the job, memory-wise. This also fixed occasional problem with accessing undefined indexes in packrat cache.
Modern code style: Codebase uses new (PHP7+) language features and code format more familiar to current modern PHP.
CLI interface is removed: Just call \hafriedlander\Peg\Compiler::compile($grammarDefinitionFile) directly however you like.
Testing: Test suite is rewritten to use Nette Tester instead of PHPUnit.
Fixed: Catastrophic backtracking problem (sometimes happening when compiling a larger grammar) avoided by simplifying regex that searches for grammar definitions.
Optimization: Using native PHP constants and functions with absolute namespace is slightly faster (changed in generated code, too).
Optimization: Use strict comparisons where possible (even in generated code).