Improve the use of the custom options

[stockiNail]

This PR is:

1. adding the options to parse function when DateTime is created by an object (was missing) in order to have a DateTime configured with user options
2. removing the options from toFormat method of Luxon because DateTime is always created with the options (see _create function)

[coveralls]

Pull Request Test Coverage Report for Build 2649783165

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 72.727%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/index.js	0	1	0.0%
<!--	Total:	0	1	0.0%	-->

Totals
Change from base Build 2085427674:	0.0%
Covered Lines:	24
Relevant Lines:	31

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💛 - Coveralls

[stockiNail]

fix #67