Add option to send email attachment from string (not only from file).

I would be very pleased if this option would be available in some
future version. Thank you.
Update version number to 2.3.7
whitespace coding standards
doublespace to single space
Merge pull request #1400 from dereuromark/master

Coding standards whitespace
bool to boolean
doc block corrections
correct return types in doc blocks
Merge pull request #1401 from dereuromark/master

CS fixes
Minor doc block improvements

http://ch1.php.net/manual/de/exception.construct.php
Second parameter gets only passed by. Exception constructor uses an int for the second parameter,not a string.

Replaced text by docblock @see
http://www.phpdoc.org/docs/latest/for-users/phpdoc/tags/see.html
Merge pull request #1402 from ravage84/patch-2

Minor doc block improvements
Update doc block.
Fixed three @param data types
Merge pull request #1404 from ravage84/patch-2

Fixed two @param data types
allow serialize in json and xml alias
Some minor CS improvements to FormHelper

Replaced use of deprecated method getVar by get.
Improved DocBocks, mostly data types
Removed deprecated DocBock tag because it's an invalid use of such. This makes the method look like it was deprecated but in reality it's only one of the possible values of one of its parameters.
Some love for a deprecated class

Whitespace and wording.

Optionally we could include a version number until when this class will work. I assumed this will be 3.0...
http://www.phpdoc.org/docs/latest/for-users/phpdoc/tags/deprecated.html
I treid that but after I let apigen generate the doc and I saw it did nothing special about it ;-/
Merge pull request #1405 from jippi/feature/_serialize-in-json-and-xml-alias

Allow serialize in json and xml alias.
Merge pull request #1407 from ravage84/patch-2

Some love for a deprecated class
Merge pull request #1406 from ravage84/formhelper

Some minor CS improvements to FormHelper