Extend the init method with a generic parameter for backend options

[2Pacalypse-]

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• run tests npm run test
• tests are included
• commit message and code follows the Developer's Certification of Origin

Checklist (for documentation change)

• only relevant documentation part is changed (make a diff before you submit the PR)
• motivation/reason is provided
• commit message and code follows the Developer's Certification of Origin

[coveralls]

Coverage remained the same at 91.436% when pulling 602f971 on 2Pacalypse-:master into 913190d on i18next:master.

[2Pacalypse-]

Ref: i18next/i18next-http-backend#103

[adrai]

lgtm...
Which version increment do you suggest for i18next and for the backends?
major, minor, patch?

[2Pacalypse-]

Probably minor.

[adrai]

thank you very much for your contribution...
all version has been released...
I will now proceed to check other backends...