Despite being a security release for Go, we do not believe Nomad is
impacted.

1.15.5 is due in a couple days but we may release before then.

Upgrade to golang 1.15

Starting with golang 1.5, setting Ctty value result in `Setctty set but Ctty not valid in child` error, as part of https://github.com/golang/go/issues/29458 .
This commit lifts the fix in https://github.com/creack/pty/pull/97 .

Go 1.14.7 fixes CVE-2020-16845 which is not believed to impact Nomad.

The Nomad binary size has been detailed differently in places
and is subject to changing almost daily. We should therefore
remove this to avoid confusion and misrepresentation.

Pick up fixes [golang 1.14.6 bug fixes](https://github.com/golang/go/issues?q=milestone%3AGo1.14.6+label%3ACherryPickApproved), specially the one where reflect.DeepEqual returns true even if values don't match, affecting our tests integrity.

Go 1.14.4 contains two CVEs which are fixed in 1.14.5:

 - [CVE-2020-15586](https://golang.org/issue/34902)
 - [CVE-2020-14039](https://golang.org/issue/39360)

Upon consideration with HashiCorp security these CVEs are considered low
severity for Nomad and no new security fix binary will be released.

- Guides now point to HashiCorp Learn, rather than old website
- Condensed the documentation & guides section for brevity
- Updated "Who Uses Nomad" page and section in README with new names collected from past 6 months
- Added yearly publication dates to each of the public talks

use hashicorp + nomad logo

Use golang 1.12.12

Use use base official golang image in CircleCI, as it gets refreshed
more quickly compared to circleci/golang, and we don't benefit from
circleci image customizations much.

To get fix for https://github.com/golang/go/issues/34540 .

Fix two broken links in the Documentation & Guides section, namely Advanced Job Scheduling on Nomad with Affinities and Increasing Nomad Fault Tolerance with Spread

The default ulimit for open files on macOS is really small (256),
which leads to "too many open files" errors during plugin launches if
you're running unit tests in `drivers/docker`. Recommend setting
`ulimit -n 1024`.

It's the latest 1.11 point release as of now