Add support for API v46.0 (forceworkbench#810)

*  Add support for API v46.0

*  Add support for API v46.0, fix wsdl files

Update constants.php

Rename wsdls to follow conventions (forceworkbench#802)

Merge pull request forceworkbench#762 from muenzpraeger/apiupgrade

Updates the API version to 43.0 for Summer '18

Fixed malformed XML

add CURLOPT_RETURNTRANSFER for version check

Merge pull request forceworkbench#740 from arthurimirzian/master

Add API v41

Merge pull request forceworkbench#702 from dmgerow/master

upgrade to api version 40

Merge pull request forceworkbench#699 from dmgerow/master

upgrade to api version 39