Upgrading guzzlehttp/guzzle 1 to 2

Bug: Custom delay time calculations are no longer ignored in the ExponentialBackoffPlugin.

Removed SSL information from the default User-Agent header.

DELETE requests can now send an entity body.

Removed the default 2mb size cutoff from the Md5ValidatorPlugin so that it now defaults to validating everything.

Bug: Query string values set to 0 are no longer dropped from the query string.

Bug: A Collection object is no longer created each time a call is made to Guzzle\Service\Command\AbstractCommand::getRequestHeaders().

Cookies are no longer URL decoded by default.

Bug: URI template variables set to null are no longer expanded.

BC: Removed magic setX methods from commands.

Verbose cURL options are no longer enabled by default.

[BC] Guzzle\Common\FromConfigInterface no longer requires any config options.

[BC] No longer supporting "{{ }}" for injecting into command or UriTemplates.

BC: Inflection classes moved to Guzzle\Inflection.

[BC] Using a custom validation system that allows a flyweight implementation for much faster validation.

[BC] Guzzle\Guzzle is now deprecated.

[BC] Simplifying Guzzle\Common\Collection.