Implement httplug

[Baachi]

I started to integrate HTTPlug into geocoder.
Current status: Its integrated but i'm not about some implentation details. For example i don't know if we really need the php-http/discovery package because it
introduce a lot of packages for a small benefit.

Reviews and thoughts are welcome!

Fixes #484 and #480

[joelwurtz]

It can be removed, httplug is now in a stable version :)

[Baachi]

Sadly no, because the discovery depends on puli which is in beta state currently 😢

[joelwurtz]

You should ignore the .puli directory

[joelwurtz]

One of the way we have done this for not having discovery, is to put discovery in suggest package then on the constructor we check the existence of the DiscoveryClass, if it has not been found we throw a \LogicException with a specific error which will be in our documentation for easy googling on that, here is an example :

if (null === $responseFactory && !class_exists('\Http\Discovery\MessageFactoryDiscovery')) {
    throw new \LogicException('No response factory provided and no discovery service is present to guess it, maybe you need to install php-http/discovery package?');
}

[Baachi]

I'm not sure about the discovery service at all, it brings many problems and puli as new dependency. Maybe we should wait for a stable release of the discovery service.

[joelwurtz]

Also CachedResponseClient can maybe be remove and use the PluginClient from php-http which provides a CachePlugin working with a PSR6 implementation.

[Baachi]

It seems puli have a problem with hhvm and php7, because travis passes for php 5.5, 5.6 but not for php7 and hhvm.

[Baachi]

Some notes: Currently the tests don't passes on PHP7 and HHVM because puli is sadly not compatible with that.
Also we must bump the requirement to php 5.5 because httplug needs at least php 5.5.

[Nyholm]

Use "php-http/discovery": "^0.8.0" and put that in require.

[smartpierre]

any updates ?

[Nyholm]

If there is interest from the maintainers to merge this, I will be happy to complete this PR.

[willdurand]

Yes, this should be merged into the lib at some point, especially because the current http lib is deprecated now.

cc @egeloen

[Nyholm]

Great. I'll try to get some work this weekend and next week.

@Baachi I hope you do not mind that I continue your work.

[Baachi]

Feel free to continue the work.

[willdurand]

See #512