This PR adds a new httpfs source driver constructor New(). It is
identical to the WithInstance() constructor but will postpone any errors
until the driver is actually being used.
This allows clients of this package to have less error checks without
loosing correctness.
In addition this PR adds more tests, improves test code coverage, and
makes golinter happy by removing deferred Close call.
This PR adds a new migration source driver capable of reading files from
any source that implements http.FileSystem interface.
Notable http.FileSystem interface implementations:
* http.Dir() - wrapper over local file-system
* github.com/shurcooL/vfsgen
Because user of this package is responsible for getting an
implementation of http.FileSystem, this driver does not support creating
instances from driver URLs.
Julius Kriukas