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/encoder.go

@@ -0,0 +1,60 @@
+package encoding
+
+import (
+	"sync"
+)
+
+// Encoder encodes the contents of v into a byte representation.
+// It's primarily used for encoding a map[string]interface{} into a file format.
+type Encoder interface {
+	Encode(v interface{}) ([]byte, error)
+}
+
+const (
+	// ErrEncoderNotFound is returned when there is no encoder registered for a format.
+	ErrEncoderNotFound = encodingError("encoder not found for this format")
+
+	// ErrEncoderFormatAlreadyRegistered is returned when an encoder is already registered for a format.
+	ErrEncoderFormatAlreadyRegistered = encodingError("encoder already registered for this format")
+)
+
+// EncoderRegistry can choose an appropriate Encoder based on the provided format.
+type EncoderRegistry struct {
+	encoders map[string]Encoder
+
+	mu sync.RWMutex
+}
+
+// NewEncoderRegistry returns a new, initialized EncoderRegistry.
+func NewEncoderRegistry() *EncoderRegistry {
+	return &EncoderRegistry{
+		encoders: make(map[string]Encoder),
+	}
+}
+
+// RegisterEncoder registers an Encoder for a format.
+// Registering a Encoder for an already existing format is not supported.
+func (e *EncoderRegistry) RegisterEncoder(format string, enc Encoder) error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	if _, ok := e.encoders[format]; ok {
+		return ErrEncoderFormatAlreadyRegistered
+	}
+
+	e.encoders[format] = enc
+
+	return nil
+}
+
+func (e *EncoderRegistry) Encode(format string, v interface{}) ([]byte, error) {
+	e.mu.RLock()
+	encoder, ok := e.encoders[format]
+	e.mu.RUnlock()
+
+	if !ok {
+		return nil, ErrEncoderNotFound
+	}
+
+	return encoder.Encode(v)
+}