* implemented validation trait for length

* converted identation to spaces

* changed the trait to not require HasLen

* added macro for generating impls

* implemented ValidateLength for some types

* using trait validation instead of the function

* added cfg for indexmap import

* changed trait to require length

* Revert "changed trait to require length"

This reverts commit a77bdc9.

* moved validation logic inside ValidateLength trait

* added trait validation for required

* added email trait validation

* fixed trait validation for email

* added range trait validation

* fixed range trait

* added url trait validation

---------

Co-authored-by: Tilen Pintarič <tilen.pintaric@aviko.si>

Keats#246)

* feat(range): add exclusive minimum and exclusive maximum for `range` validation

* test(range): add tests for `exc_min` and `exc_max` range validation

* docs: add docs for `exc_min` and `exc_max` for `range` validation

* chore: rename `exc_min`, `exc_max` to `exclusive_min`, `exclusive_max`

* chore(validation.rs): get rid of `collide` function

…kind

This makes it possible for code consuming the constraints to know
whether the type is used directly or if it is held in some kind of
collection.