Add wait_until_ready config and check if phiremock server is actually running

[barell]

This PR adds:

• new configs: wait_until_ready and wait_until_ready_timeout
• if wait_until_ready is set to true it will use phiremock client reset method to call phiremock server
• if phiremock server does not respond within specified timeout, exception will be thrown
• some updates to README

[barell]

This is to fix issue: #47

[barell]

Made some further improvements to this PR. It can now use Phiremock Client and fallback to curl request. If both Phiremock client and curl extension are not present and wait_until_ready is set to true it will throw exception.

[mcustiel]

@barell thank you very much for your support to phiremock and sorry for the delay to review/merge your PR.

[barell]

Awesome, thanks @mcustiel