fix(Config): colorization without pager (#687)

Fix an issue whereby colorization would output ANSI codes if a pager was
not configured.

The solution here is to stop guessing about the state of the user's
system at runtime, as well as the user's intention. The installer now
chooses an appropriate installer when generating configs, and no longer
bothers searching for pagers at runtime.

internal/config/pager.go

@@ -0,0 +1,26 @@
+package config
+
+import (
+	"os"
+	"os/exec"
+)
+
+// Pager attempts to locate a pager that's appropriate for the environment.
+func Pager() string {
+
+	// if $PAGER is set, return the corresponding pager
+	if os.Getenv("PAGER") != "" {
+		return os.Getenv("PAGER")
+	}
+
+	// Otherwise, search for `pager`, `less`, and `more` on the `$PATH`. If
+	// none are found, return an empty pager.
+	for _, pager := range []string{"pager", "less", "more"} {
+		if path, err := exec.LookPath(pager); err != nil {
+			return path
+		}
+	}
+
+	// default to no pager
+	return ""
+}