Implement Cobra CLI tooling, Viper config tooling (#336)

* start pulling out + replacing urfave and config

* replace many many instances of config

* move more stuff => viper

* properly remove urfave

* move some flags to root command

* add testrig commands to root

* alias config file keys

* start adding cli parsing tests

* reorder viper init

* remove config path alias

* fmt

* change config file keys to non-nested

* we're more or less in business now

* tidy up the common func

* go fmt

* get tests passing again

* add note about the cliparsing tests

* reorganize

* update docs with changes

* structure cmd dir better

* rename + move some files around

* fix dangling comma

internal/config/viper.go

@@ -0,0 +1,42 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package config
+
+import (
+	"strings"
+
+	"github.com/spf13/pflag"
+	"github.com/spf13/viper"
+)
+
+func InitViper(f *pflag.FlagSet) error {
+	// environment variable stuff
+	// flag 'some-flag-name' becomes env var 'GTS_SOME_FLAG_NAME'
+	viper.SetEnvPrefix("gts")
+	viper.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
+	viper.AutomaticEnv()
+
+	// flag stuff
+	// bind all of the flags in flagset to viper so that we can retrieve their values from the viper store
+	if err := viper.BindPFlags(f); err != nil {
+		return err
+	}
+
+	return nil
+}