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

vendor/github.com/spf13/viper/internal/encoding/decoder.go

@@ -0,0 +1,61 @@
+package encoding
+
+import (
+	"sync"
+)
+
+// Decoder decodes the contents of b into a v representation.
+// It's primarily used for decoding contents of a file into a map[string]interface{}.
+type Decoder interface {
+	Decode(b []byte, v interface{}) error
+}
+
+const (
+	// ErrDecoderNotFound is returned when there is no decoder registered for a format.
+	ErrDecoderNotFound = encodingError("decoder not found for this format")
+
+	// ErrDecoderFormatAlreadyRegistered is returned when an decoder is already registered for a format.
+	ErrDecoderFormatAlreadyRegistered = encodingError("decoder already registered for this format")
+)
+
+// DecoderRegistry can choose an appropriate Decoder based on the provided format.
+type DecoderRegistry struct {
+	decoders map[string]Decoder
+
+	mu sync.RWMutex
+}
+
+// NewDecoderRegistry returns a new, initialized DecoderRegistry.
+func NewDecoderRegistry() *DecoderRegistry {
+	return &DecoderRegistry{
+		decoders: make(map[string]Decoder),
+	}
+}
+
+// RegisterDecoder registers a Decoder for a format.
+// Registering a Decoder for an already existing format is not supported.
+func (e *DecoderRegistry) RegisterDecoder(format string, enc Decoder) error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	if _, ok := e.decoders[format]; ok {
+		return ErrDecoderFormatAlreadyRegistered
+	}
+
+	e.decoders[format] = enc
+
+	return nil
+}
+
+// Decode calls the underlying Decoder based on the format.
+func (e *DecoderRegistry) Decode(format string, b []byte, v interface{}) error {
+	e.mu.RLock()
+	decoder, ok := e.decoders[format]
+	e.mu.RUnlock()
+
+	if !ok {
+		return ErrDecoderNotFound
+	}
+
+	return decoder.Decode(b, v)
+}