Prop for auto-placement of items list

[blint96]

When typeahead input is on bottom of page and user open typeahead hints, many of them are out of screen.
This is my solution of this problem.

When input is on first 50% of viewport height, list displays as always to the bottom but when input is on second 50% of viewport height, list goes above the input.

Thank you for your involvement in open-source solutions and I'll be glad if you find my PR helpful.

[coveralls]

Pull Request Test Coverage Report for Build 97

• 0 of 5 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-5.8%) to 63.551%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/components/VueBootstrapTypeahead.vue	0	5	0.0%

Totals
Change from base Build 38:	-5.8%
Covered Lines:	47
Relevant Lines:	73

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💛 - Coveralls