main: switch to urfave/cli/v2

For now this is a drop in replacement for all the flags curently
implemented

Fixes: #171

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/github.com/urfave/cli/v2/README.md

@@ -0,0 +1,70 @@
+cli
+===
+
+[![GoDoc](https://godoc.org/github.com/urfave/cli?status.svg)](https://pkg.go.dev/github.com/urfave/cli/v2)
+[![codebeat](https://codebeat.co/badges/0a8f30aa-f975-404b-b878-5fab3ae1cc5f)](https://codebeat.co/projects/github-com-urfave-cli)
+[![Go Report Card](https://goreportcard.com/badge/urfave/cli)](https://goreportcard.com/report/urfave/cli)
+[![codecov](https://codecov.io/gh/urfave/cli/branch/master/graph/badge.svg)](https://codecov.io/gh/urfave/cli)
+
+cli is a simple, fast, and fun package for building command line apps in Go. The
+goal is to enable developers to write fast and distributable command line
+applications in an expressive way.
+
+## Usage Documentation
+
+Usage documentation exists for each major version. Don't know what version you're on? You're probably using the version from the `master` branch, which is currently `v2`.
+
+- `v2` - [./docs/v2/manual.md](./docs/v2/manual.md)
+- `v1` - [./docs/v1/manual.md](./docs/v1/manual.md)
+
+Guides for migrating to newer versions:
+
+- `v1-to-v2` - [./docs/migrate-v1-to-v2.md](./docs/migrate-v1-to-v2.md)
+
+## Installation
+
+Using this package requires a working Go environment. [See the install instructions for Go](http://golang.org/doc/install.html).
+
+Go Modules are required when using this package. [See the go blog guide on using Go Modules](https://blog.golang.org/using-go-modules).
+
+### Using `v2` releases
+
+```
+$ GO111MODULE=on go get github.com/urfave/cli/v2
+```
+
+```go
+...
+import (
+  "github.com/urfave/cli/v2" // imports as package "cli"
+)
+...
+```
+
+### Using `v1` releases
+
+```
+$ GO111MODULE=on go get github.com/urfave/cli
+```
+
+```go
+...
+import (
+  "github.com/urfave/cli"
+)
+...
+```
+
+### GOPATH
+
+Make sure your `PATH` includes the `$GOPATH/bin` directory so your commands can
+be easily used:
+```
+export PATH=$PATH:$GOPATH/bin
+```
+
+### Supported platforms
+
+cli is tested against multiple versions of Go on Linux, and against the latest
+released version of Go on OS X and Windows. This project uses Github Actions for
+builds. To see our currently supported go versions and platforms, look at the [./.github/workflows/cli.yml](https://github.com/urfave/cli/blob/master/.github/workflows/cli.yml).