Breaking change: SDK v2

[kmoe]

closes #38

Upgrade SDK to v2.0.3

Enable binary acceptance test driver with reattach testing.

Absolute paths are now required for local filesystem resources created and checked during tests; use temporary directories for this purpose.

• Match scaffolding provider directory layout
• Remove outdated website targets in Makefile
• Update Go version for development and CI

[kmoe]

This PR has been repurposed as the SDKv2 upgrade, as that supersedes the earlier upgrade to binary testing.

[kmoe]

The acceptance test failure is due to a bug introduced in Terraform 0.13, in which data sources with references to resources get evaluated too early.

With Terraform 0.11.0 and 0.12.20, the following config produces a file called local_file on terraform apply:

resource "local_file" "file" {
  content  = "This is some content"
  filename = "local_file"
}
data "local_file" "file" {
  filename = "${local_file.file.filename}"
}

With Terraform 0.13.3, terraform apply produces the following error:

❤ @up ➜  localdata  terraform apply

Error: open local_file: no such file or directory

  on main.tf line 5, in data "local_file" "file":
   5: data "local_file" "file" {

I think this is fixed in hashicorp/terraform#26458, not yet released. In any case, the problem is fixed in terraform built from 78322d5843daf76b72d6023a39094642f8d69886. Our options are:

1. Wait until the fix is in latest stable Terraform 0.13 release, at which point the acc tests will pass as the latest stable version is automatically pulled in.
2. Update this provider's CI to use that git ref to build the version of Terraform used in tests (and remove that later).
3. Remove or change the test so it doesn't trigger this bug.

@paultyng, I'm happy with (1), but if we want to get this merged soon then (3) is probably more sensible.

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