func isSpace(r rune) bool {
	switch r {
	case ' ', '\t':
		return true
	default:
		return false
	}
}
isSpace checks whether the rune represents space or not.
Only white spcaes (U+0020) and horizontal tabs are treated as space character.
It is the same as Go.

See https://github.com/MakeNowJust/heredoc/issues/6#issuecomment-524231625.
package heredoc
import (
	"fmt"
	"strings"
)
const maxInt = int(^uint(0) >> 1)
func Doc(raw string) string {
	skipFirstLine := false
	if len(raw) > 0 && raw[0] == '\n' {
		raw = raw[1:]
	} else {
		skipFirstLine = true
	}
	rawLines := strings.Split(raw, "\n")
	lines := rawLines
	if skipFirstLine {
		lines = lines[1:]
	}
	minIndentSize := getMinIndent(lines)
	lines = removeIndentation(lines, minIndentSize)
	return strings.Join(rawLines, "\n")
}