Add basic support for expressing algorithms in positionless form.

[lucteo]

Created an iterator that maps to positionless operations. Currently we only support forward and backward access (no random access).

[RishabhRD]

Few comments on contracts

[RishabhRD]

One thing to notice here is, the complexity of algorithms in this case totally depends on assumption that algorithm_data would contain potentially bounded and small number of iterators information.
The good thing is that's usually the case atleast the algorithms I remember follows the same. However, it might be interesting if we can find any counter-example to that. I really feel if they exist, those algorithms should be really rare.

[RishabhRD]

LGTM!