chore: DRY out colorization code

Creates a `sheet.Colorize` method that DRYs out code that was duplicated
among `cmd_search` and `cmd_view`.

internal/sheet/colorize.go

@@ -0,0 +1,37 @@
+package sheet
+
+import (
+	"bytes"
+
+	"github.com/cheat/cheat/internal/config"
+
+	"github.com/alecthomas/chroma/quick"
+)
+
+// Colorize applies syntax-highlighting to a cheatsheet's Text.
+func (s *Sheet) Colorize(conf config.Config) {
+
+	// if the syntax was not specified, default to bash
+	lex := s.Syntax
+	if lex == "" {
+		lex = "bash"
+	}
+
+	// write colorized text into a buffer
+	var buf bytes.Buffer
+	err := quick.Highlight(
+		&buf,
+		s.Text,
+		lex,
+		conf.Formatter,
+		conf.Style,
+	)
+
+	// if colorization somehow failed, do nothing
+	if err != nil {
+		return
+	}
+
+	// otherwise, swap the cheatsheet's Text with its colorized equivalent
+	s.Text = buf.String()
+}