wip modernize code base

vendor/github.com/kelseyhightower/envconfig/README.md

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+# envconfig
+
+[![Build Status](https://travis-ci.org/kelseyhightower/envconfig.svg)](https://travis-ci.org/kelseyhightower/envconfig)
+
+```Go
+import "github.com/kelseyhightower/envconfig"
+```
+
+## Documentation
+
+See [godoc](http://godoc.org/github.com/kelseyhightower/envconfig)
+
+## Usage
+
+Set some environment variables:
+
+```Bash
+export MYAPP_DEBUG=false
+export MYAPP_PORT=8080
+export MYAPP_USER=Kelsey
+export MYAPP_RATE="0.5"
+export MYAPP_TIMEOUT="3m"
+export MYAPP_USERS="rob,ken,robert"
+export MYAPP_COLORCODES="red:1,green:2,blue:3"
+```
+
+Write some code:
+
+```Go
+package main
+
+import (
+    "fmt"
+    "log"
+    "time"
+
+    "github.com/kelseyhightower/envconfig"
+)
+
+type Specification struct {
+    Debug       bool
+    Port        int
+    User        string
+    Users       []string
+    Rate        float32
+    Timeout     time.Duration
+    ColorCodes  map[string]int
+}
+
+func main() {
+    var s Specification
+    err := envconfig.Process("myapp", &s)
+    if err != nil {
+        log.Fatal(err.Error())
+    }
+    format := "Debug: %v\nPort: %d\nUser: %s\nRate: %f\nTimeout: %s\n"
+    _, err = fmt.Printf(format, s.Debug, s.Port, s.User, s.Rate, s.Timeout)
+    if err != nil {
+        log.Fatal(err.Error())
+    }
+
+    fmt.Println("Users:")
+    for _, u := range s.Users {
+        fmt.Printf("  %s\n", u)
+    }
+
+    fmt.Println("Color codes:")
+    for k, v := range s.ColorCodes {
+        fmt.Printf("  %s: %d\n", k, v)
+    }
+}
+```
+
+Results:
+
+```Bash
+Debug: false
+Port: 8080
+User: Kelsey
+Rate: 0.500000
+Timeout: 3m0s
+Users:
+  rob
+  ken
+  robert
+Color codes:
+  red: 1
+  green: 2
+  blue: 3
+```
+
+## Struct Tag Support
+
+Envconfig supports the use of struct tags to specify alternate, default, and required
+environment variables.
+
+For example, consider the following struct:
+
+```Go
+type Specification struct {
+    ManualOverride1 string `envconfig:"manual_override_1"`
+    DefaultVar      string `default:"foobar"`
+    RequiredVar     string `required:"true"`
+    IgnoredVar      string `ignored:"true"`
+    AutoSplitVar    string `split_words:"true"`
+    RequiredAndAutoSplitVar    string `required:"true" split_words:"true"`
+}
+```
+
+Envconfig has automatic support for CamelCased struct elements when the
+`split_words:"true"` tag is supplied. Without this tag, `AutoSplitVar` above
+would look for an environment variable called `MYAPP_AUTOSPLITVAR`. With the
+setting applied it will look for `MYAPP_AUTO_SPLIT_VAR`. Note that numbers
+will get globbed into the previous word. If the setting does not do the
+right thing, you may use a manual override.
+
+Envconfig will process value for `ManualOverride1` by populating it with the
+value for `MYAPP_MANUAL_OVERRIDE_1`. Without this struct tag, it would have
+instead looked up `MYAPP_MANUALOVERRIDE1`. With the `split_words:"true"` tag
+it would have looked up `MYAPP_MANUAL_OVERRIDE1`.
+
+```Bash
+export MYAPP_MANUAL_OVERRIDE_1="this will be the value"
+
+# export MYAPP_MANUALOVERRIDE1="and this will not"
+```
+
+If envconfig can't find an environment variable value for `MYAPP_DEFAULTVAR`,
+it will populate it with "foobar" as a default value.
+
+If envconfig can't find an environment variable value for `MYAPP_REQUIREDVAR`,
+it will return an error when asked to process the struct.  If
+`MYAPP_REQUIREDVAR` is present but empty, envconfig will not return an error.
+
+If envconfig can't find an environment variable in the form `PREFIX_MYVAR`, and there
+is a struct tag defined, it will try to populate your variable with an environment
+variable that directly matches the envconfig tag in your struct definition:
+
+```shell
+export SERVICE_HOST=127.0.0.1
+export MYAPP_DEBUG=true
+```
+```Go
+type Specification struct {
+    ServiceHost string `envconfig:"SERVICE_HOST"`
+    Debug       bool
+}
+```
+
+Envconfig won't process a field with the "ignored" tag set to "true", even if a corresponding
+environment variable is set.
+
+## Supported Struct Field Types
+
+envconfig supports these struct field types:
+
+  * string
+  * int8, int16, int32, int64
+  * bool
+  * float32, float64
+  * slices of any supported type
+  * maps (keys and values of any supported type)
+  * [encoding.TextUnmarshaler](https://golang.org/pkg/encoding/#TextUnmarshaler)
+  * [encoding.BinaryUnmarshaler](https://golang.org/pkg/encoding/#BinaryUnmarshaler)
+  * [time.Duration](https://golang.org/pkg/time/#Duration)
+
+Embedded structs using these fields are also supported.
+
+## Custom Decoders
+
+Any field whose type (or pointer-to-type) implements `envconfig.Decoder` can
+control its own deserialization:
+
+```Bash
+export DNS_SERVER=8.8.8.8
+```
+
+```Go
+type IPDecoder net.IP
+
+func (ipd *IPDecoder) Decode(value string) error {
+    *ipd = IPDecoder(net.ParseIP(value))
+    return nil
+}
+
+type DNSConfig struct {
+    Address IPDecoder `envconfig:"DNS_SERVER"`
+}
+```
+
+Also, envconfig will use a `Set(string) error` method like from the
+[flag.Value](https://godoc.org/flag#Value) interface if implemented.