feature #4159 [WCM][OptionsResolver] Adjusted the OptionsResolver documentation to describe the 2.6 API (webmozart, peterrehm)

This PR was merged into the master branch.

Discussion
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[WCM][OptionsResolver] Adjusted the OptionsResolver documentation to describe the 2.6 API

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#11716, symfony/symfony#12156)
| Applies to    | 2.6+
| Fixed tickets | -

Commits
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575c320 Updated OptionsResolver documentation: removed static methods
fab825d Merge pull request #1 from peterrehm/patch-9
f202fb8 Removed duplicate use statements
ae66893 Added missing mailer class and use statements
43ae1d8 [OptionsResolver] Adjusted the OptionsResolver documentation to describe the 2.6 API

Author: weaverryan