Add 'imapFrom' function and family

[chshersh]

Sometimes user needs to start mapping not from zero but from one. With old zip solution you can just replace zip [0..] with zip [1..] but there's no simple way to do it with ilist package. Source code of imap function gives clear way how to implement this function. And imap can be defined in terms of imapFrom without loss of performance most likely.

Well, it seems like a lot of functions can have *from version. If this change is too radical than I can propose to add such function per issue request.