[vers] how to deal with problematic symbols such as brackets

[prabhu]

The vers specification is lacking some guidance regarding version specifiers with problematic symbols such as brackets.

https://github.com/package-url/purl-spec/blob/master/VERSION-RANGE-SPEC.rst

Example:

vers:foo/<=2.0\(0.249\)
vers:foo/!=10.4\(2\)
vers:foo/>2.1\(0.474\)|<2.2\(1.145\)

NVD feeds escapes such characters with a double slash. We currently store them escaped with a single slash, but not sure what the correct approach must be.