Improve parser errors

[batiati]

Parser errors are very limited, and they have few test cases.
There are some missing features in parser errors:

• Closing tags are not checked, you can open a tag with triple-mustaches and close with regular ones {{{invalid}}
• Define the correct behavior when dealing with triple-mustaches and custom delimiters, for now, any delimiter + { is recognized as a triple-mustache
• Improve error messages, maybe by printing parser errors on the output writer when rendering in the streamed mode and comptime mode.