The variable scope in the Go templates makes it hard, if possible at all, to write templates with counter variables or similar state.
This commit fixes that by adding a writable context to Node, backed by a map: Scratch.
This context has three methods, Get, Set and Add. The Add is tailored for counter variables, but can be used for any built-in numeric values or strings.
File handling was broken on Windows. This commit contains a revision of the path handling with separation of file paths and urls where needed.
There may be remaining issues and there may be better ways to do this, but it is easier to start that refactoring job with a set of passing tests.
Fixes #687
Fixes #660
