Add EveryOther extension methods
* One takes a func, one takes an action
* Both have a bool, for whether first operation should happen on zeroth, or first
Add a skip predicate to EveryOther
Also add a non-generic EveryOther for strings that wraps the
`new string(stuff.ToArray())` stuff you have to do so we don't have to
do that every time
Merge pull request #14 from awseward/collections_every_other

Collections every other