Add MethodCodeElement
Rename PHPAnalyzer to CodeAnalyzer, and CustomResourceAnalyzer to ResourceAnalyzer

To align better with CodeElement, and ResourceElement. Also rename files.
Add HACKING.md containing a 'Glossary' and a 'Code Walkthrough'
Modify CodeAnalyzer and ResourceAnalyzer to directly operate on a node tree

To that end, an AnalyzerVisitor is used to create elements for relevant nodes
using two new factories, CodeElementFactory and ResourceElementFactory.
Remove AnalyzedPHPFileTest as it's obsolete

The interface ("code element hierarchy") it is testing is not used by VIP-scanner
anymore; instead, the node tree itself is traversed by analyzers.
Remove vip-scanner/class-token-parser.php as it's obsolete now