* usage of `Apply` sans placeholders was already possible and as such duplicated `utility::defer_eval`
* renamed `apply_none`'s type alias from to `type` to enable combining it with `Eval`

* `ListIndex` already implements the necessary partial template specializations for finding elements matching a predicate
* reimplemented `Cond` using `detail::find_variadic` as `Find` depends on `Apply` which in turn depends on `Cond`
** it is useful if core functionality such as the branched conditional `Cond` do not require higher order functionality such as `Find`
*** otherwise one can not use core functionality in the implementation of higher order functionality
* introduced `utility::predicate_guard` helper template
** checks a given value using a predicate and only forwards the value to the guarded function if this check is successful
** if check is unsuccessful it returns a surrogate value simmilar to `utility::predicate_assurance`

* new higher order list operation `ListIndex` returns the index of the first list element satisfying a given predicate function
** this enables finding the split index required for both `TakeWhile` and `DropWhile`
** actual list manipulation is then performed using lower order `Take` or `Drop`
** analogously to `list-index` in SRFI-1
** added appropriate test case
* added higher order predicate utility function `utility::predicate_assurance`
** as its name implies this function enables assuring that a value satisfies a given predicate
*** if this is not the case a surrogate value is returned instead
** this is used to return a appropriate size value if the `ListIndex` call fails because no element satisfies its predicate
** `detail::predicate_negator` was moved from `Remove`'s implementation details into the newly introduced `utility` namespace
*** as it is required by both `TakeWhile` and `DropWhile` in addition to `Remove`
* continuation of 8e49cc6