curl will be installed to all AppVeyor build workers into separate folder and added to PATH.

• Download location: https://bintray.com/vszakats/generic/curl/7.53.1
• Installation location: C:\Tools\curl
• Should be added into beginning of PATH variable to have highest priority
• Update installed software page on website
• Check that pre-installed curl is not conflicting with the one installed by Chocolatey