GitLab

* vendor Azure Go SDK (#210)

* vendor the Azure Go SDK and dependencies

* add initial Azure DNS provider implementation (#210)

* add 'azure' value to 'provider' command line option
* add 'azure-config-file' command line option
* add 'azure-resource-group' command line option
* implement initial Azure DNS provider

note: azure provider is not yet fully implemented (does not query for existing
records).

tests and documentation are forthcoming.

* add a tutorial for the Azure provider (#210)

* add tutorial for using ExternalDNS with Azure DNS

* finish implementation of Azure DNS provider (#210)

* implement the Records method for the Azure DNS provider

* refactor Azure API interface for future tests (#210)

* make Azure provider use an interface for future unit tests

* add unit tests for the Azure provider (#210)

* test retrieving Azure DNS records.
* test updating and deleting Azure DNS records.
* test dry run for the Azure provider (i.e. noop).