Use PHP-Parser instead of our own one

If PHP parsing fails, display a blocker type error.
Write ScopeVisitor to add scope information to node.
For future use by analyzers and scanners, have AnalyzedPHPFile
expose its AST via get_node_tree().
Add InAssignmentVisitor to provide the 'in_var' attribute
Turn renderers into elements

Turn the renderers (except for the underlying AnalyzerRenderer) into 'elements',
which are given a Node (or subclass thereof; or filename, in case of
FileElement) object at construction time, and whose sole purpose is then to
make information available in a way that can be easily represented by
AnalyzerRenderer.
Rename renderers to elements, and move files accordingly
Clean up PHPDoc strings
Handle method and static calls separately from regular function calls
Add ClassMethodCodeElement
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