Exception added

Added Exception SMTP_Validate_Email_Exception_Send_Failed.
Merge pull request #4 from Webysther/patch-1

Added missing Exception
Greylisted expected codes fix.
Merge pull request #6 from kevin39/master

Greylisted expected codes fix.
Increased default RSET timeout - fixes #7
Misc enhancements & fixes

* Timeout improved after intensive tests
* Log attribute set to public for debug purposes
* Ability to disable catch all testing (catchall_test)
* Timeout are now catched properly (flag email as valid) in case
to accept down in case to avoid false positive
* Better support for RSET, NOOP and QUIT on weird RFC
implementations
* Added catch to handle empty/non-response
Improved codes

* Added constant for codes 500, 502 and 503
* Replaced tabs with spaces
* expect() returns en Unexpected exception instead of
no response in case of empty response
Merge pull request #10 from kevin39/master

Misc enhancements & fixes:

- reduced some timeouts, added ability to skip catch-all testing, expect() tweaks..
Minor whitespace/docblocks/syntax tweaks after #10
Handle @kevin39's #10 exception catching slightly differently, maintaining configurable results when comm fails...

...instead of assuming everything is valid when those exceptions occur.
Controlling the desired outcome is done via `$this->no_comm_is_valid`, as before.
Update README.md
Merge pull request #1 from zytzagoo/master

update