[OptionsResolver] Adjusted the OptionsResolver documentation to describe the 2.6 API
Added missing mailer class and use statements
Removed duplicate use statements
Merge pull request #1 from peterrehm/patch-9

Added mailer class and use statements
Added config example for Varnish 4.0
add sidebar for the built-in server in VMs
Removed extra parenthesis
fix route prefix in PHP code example
[Serializer] Handle circular references. symfony/symfony#12098.
Missing space
Remove incoherence between Doctrine and Propel introduction paragraphs
bug #4350 Removed extra parenthesis (sivolobov)

This PR was merged into the 2.3 branch.

Discussion
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Removed extra parenthesis

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?  | no
| Applies to    | all versions
| Fixed tickets | no tickets

Commits
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6e9e1e6 Removed extra parenthesis
minor #4355 Missing space (ErikSaunier)

This PR was merged into the 2.3 branch.

Discussion
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Missing space

Commits
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7ae8285 Missing space
fix Twig-extensions links
Fixed link to documentation standards
minor #4358 Fixed link to documentation standards (sivolobov)

This PR was merged into the 2.3 branch.

Discussion
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Fixed link to documentation standards

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs? | no
| Applies to   | all versions
| Fixed tickets | no tickets

Commits
-------

49e5dad Fixed link to documentation standards
Added missing closing parenthesis to example.
minor #4359 Added missing closing parenthesis to example. (mattjanssen)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4359).

Discussion
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Added missing closing parenthesis to example.

Commits
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d1bfa91 Added missing closing parenthesis to example.
minor #4357 fix Twig-extensions links (mhor)

This PR was merged into the 2.3 branch.

Discussion
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fix Twig-extensions links

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | -

related https://github.com/twigphp/Twig/pull/1554, https://github.com/twigphp/Twig-extensions/pull/123

Commits
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82ea9df fix Twig-extensions links
Missing apostrophe in source example.