Expression overhaul

This mayor release contains a mayor rewrite of the expression parser, adding an tokenizer that greatly simplifies the tokenizing and parsing steps for expressions. This also results in a 20% performance improvement in small-medium sized expressions (<500 chars) but is slower for larger expressions. It also fixes a lot of bugs with the experimental operator feature and adds brackets for expressions.

• Added predefined Path formatter
• allows brackets in expressions
• Added AsObject formatter to convert IDictionary<string, object> into c# objects
• Added null placeholder update within template by setting the $null variable: {{#var $null = 'DD'}}
• Added Expression tokenizer and parser

this is an pre-release as there will be some performance improvements but it should be considered production ready.