Add InList and NotInList

[fahimbagar]

This PR does the following:

• Add InList and NotInList for given types:
  • Value
  • Object
  • Array
  • String
  • Number
  • Boolean (just for completeness)
  • Duration
  • DateTime
    -Since AssertionList rejects a single slice as a param, single array param in InList will behave like IsEqual and NotInList will behave like NotEqual. Addressed in commit 649ee8c

httpexpect/assertion_validation.go

Lines 186 to 190 in 86f366a

	if len(lst) == 1 && reflect.ValueOf(lst[0]).Kind() == reflect.Slice {
	return errors.New(
	"AssertionList should contain a list of values," +
	" but it contains a single element which itself is a list")
	}

For issue #250

[coveralls]

Coverage: 94.8% (+0.2%) from 94.555% when pulling 0d5cba1 on fahimbagar:add-InList-and-NotInList into 86f366a on gavv:master.

[gavv]

Thanks for update! A few comments

[gavv]

Thanks!

[gavv]

Small follow-up commit: 8fe2ffb

[gavv]

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