Escaping curly braces, vertical bars, and angle brackets in record-based nodes

[marc-reh]

I would like to suggest the addition of curly braces, vertical bars and angle brackets to the definition of escape letters (letters for which a preceding slash is not escaped).

In Printing.hs:

escLetters = Set.fromList ['N', 'G', 'E', 'T', 'H', 'L', 'n', 'l', 'r','{','}','|','<','>']

See also http://www.graphviz.org/doc/info/shapes.html#record

[ivan-m]

Except there is explicit support for record labels already.

This escape list is used everywhere for the definition of strings (e.g. identifiers), not just for labels, so it can't be used like that.

[marc-reh]

I wasn't aware of the explicit support for record labels. Using them, I don't need to escape curly braces etc. anymore and can use graphviz as is. Thanks!