v0.37.0

Most relevant commits:

• templates/builtin: add global functions to use in templates
• cmd/scriggo: use Scriggo builtins serving templates
• compiler: make 'for in' statement iterate over the keys of a map
• compiler/checker: fix error type checking 'for in' on channel
• cmd/scriggo: fix error while building an interpreter
• cmd/scriggo: change module path
• cmd/scriggo: add "runtime/metrics" package to stdlib