Fix issue #8: Add support for Some(*patterns) that matches subsequences

[scravy]

This allows Some(*) to match subsequences.

Previously Some(...) would only match individiual items, i.e. the pattern [0, Some(1), 2] would match the value [0, 1, 1, 1, 2]. Compared with a regex on strings this would be like 01*2 but the repetition here could not be applied to subsequences 0(12)*3. This pull request introduces the ability for Some(*) to take multiple patterns which it then tries to match as a sequence within: [0, Some(1, 2), 3] would now match the value [0, 1, 2, 1, 2, 3]. This could not be expressed before.

Note that the new syntax is different from Some([1, 2]) as this would match items which are themselves lists, i.e. [0, [1, 2], [1, 2], 3].