Improve expression type parsing

[erwinvaneyk]

Currently implicit expressions are recognized only when there is a trailing $. This lacks flexibility in the expressions. There should be ways to improve this identification of expression types vs. regular strings.

[erwinvaneyk]

Current proposed solution (credits @soamvasani) is to use "{...}" to mark a string as an expression. It 'abuses' the fact that in javascript {<expr>} == <expr> to avoid the need to parse the expression before feeding it to Otto.

[erwinvaneyk]

Fixed. Current solution is a {<expr>} syntax.