Fix accessing calls

Some plugins need access to the handler (and rewriter) calls. One
example is the do plugin.

This adds some accessing methods to the callWriter objects, ensures
$calls can be acc

Fix accessing calls

Some plugins need access to the handler (and rewriter) calls. One
example is the do plugin.

This adds some accessing methods to the callWriter objects, ensures
$calls can be accessed and removes some duplicate code by introducing an
abstract base class.

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Make lexer/state stack more understandable
- rename lexer $mode property to avoid two different uses of "mode"
variables in the lexer
- clarify/improve comments

moved all parsing related namespaces to their own