Implement regular expressions

[71104]

The syntax still needs to be defined.

Delimiting with slashes (like in JavaScript) causes syntax ambiguities (like in JavaScript).

On the other hand there aren't many other available symbols to use as delimiters, most have been used for operators (and that design is not going to change).

[71104]

Valid option for the delimiters: the dollar symbol ($).

Example: $foo$.test "is this foo?"

[71104]

The "at" symbol (@) would be another option but it is going to be used for annotations.

[71104]

Now that #73 is fixed, more symbols have become available by the way.