Use .eml extensions for emails stored with Zend\Mail\Transport\File

The widely used extension for mime emails in plain text is .eml [1]
This commit changes the currently used .tmp extension to .eml as .tmp does not make much sense in this case anyway.

By doing this one could open directly the email with the associated user agent (eg: by double clicking the file in the file browser).

[1] https://en.wikipedia.org/wiki/Email#Filename_extensions
Changed the regexp used in the FileOptions transport tests.
allow replacing elements within a form collection

currently you can only remove elements by submitting fewer elements than is requested. this patch will allow you to replace elements i.e. remove an element and add another one.
tests to rmove and replace form collection elements
Update MemoryManager.php

Renamed private function to new naming convention.

Missing: _create
Update Feed.php

Rename private methods to new naming convention
Hydrator contains two responsibilities it is Hydration and Extraction, my suggestion is to segregate this responsibilities at least with Interfaces.
Fix spelling of "marshall"

"Marshall" is a proper noun.  The verb you were going for is "marshal" (one "L").
make use of mickey179/vfsStream in unit tests: Zend\Test
add test populateValues with traversable
added testcase for nested Traversable values with nested fieldset
fix value of nested fieldset can be a Traversable
added missing newline
removed @package from docblock
Mime\Message: createFromString: really ignore unknown headers
Add assertTemplateName and assertNotTemplateName
cs fix
PartialLoop helper: prevent convert traversable model to array recursively

I consider when we pass a model as traversable to partial loop, we don't need to convert it to array recursively.
For example, when we pass a form collection (of fieldsets) to partial loop as the model, if we converted it to array recursively -> fieldsets will converted to array too, in view script we can't access the fieldset through object key.
Updated Zend\Form\Factory, prepareAndInjectElements() continue on null element specification
Issue 4662 - Zend\Db\PDO adapter driver ignores charset option