Add docs for mcrypt/openssl migration and how to do it.
Clarify Custom Type docs.

Refs #2162
Remove mcrypt requirement.

CakePHP doesn't require mcrypt anymore. It can use either openssl, or
mcrypt.
Merge pull request #2170 from cakephp/issue-2162

Clarify Custom Type docs.
[fr] 3c5b4cf
PSR-2ify function example
PSR-2ify class example
add blank line after "use" statement
some forgotten functions
Merge pull request #2169 from cakephp/mcrypt-docs

Add docs for mcrypt/openssl migration and how to do it.
Merge pull request #2167 from antograssiot/3.0-psr2-code-sample

3.0 psr2 code sample