Reimplement existing validators as fluent, core feature

[fushar]

We have started writing some number and vector validators as individual functions.

We want to convert the existing validators to become "fluent", so that:

• It can benefit from compiler autocomplete feature
• To prepare for future graph/tree validators

We also want to make them as "core" feature, i.e. users don't have to include any other headers.

List of changes:

Before	After
isBetween(n, a, b)	valueOf(n).isBetween(a, b)
eachElementIsBetween(v, a, b)	eachElementOf(v).isBetween(a, b)
elementsAreAscending(v)	elementsOf(v).areAscending()
elementsAreDescending(v)	elementsOf(v).areDescending()
elementsAreNonAscending(v)	elementsOf(v).areNonAscending()
elementsAreNonDescending(v)	elementsOf(v).areNonDescending()
elementsAreUnique(v)	elementsOf(v).areUnique()