Fix various bugs around word splitting (#51)

* Fix various bugs around word splitting

Impacts:
* option names splitting
* command alias splitting
* Env var name splitting

Bug:
A naive `strings.Split(val, " ")` was performed to split a value into words.
If a values contains 2+ spaces, an empty value is returned in the word list.

commands.go

@@ -104,7 +104,7 @@ the last argument, init, is a function that will be called by mow.cli to further
 (sub) command, e.g. to add options, arguments and the code to execute
 */
 func (c *Cmd) Command(name, desc string, init CmdInitializer) {
-	aliases := strings.Split(name, " ")
+	aliases := strings.Fields(name)
 	c.commands = append(c.commands, &Cmd{
 		ErrorHandling: c.ErrorHandling,
 		name:          aliases[0],
@@ -389,7 +389,7 @@ func (c *Cmd) formatDescription(desc, envVar string) string {
 	if len(envVar) > 0 {
 		b.WriteString(" (")
 		sep := ""
-		for _, envVal := range strings.Split(envVar, " ") {
+		for _, envVal := range strings.Fields(envVar) {
 			b.WriteString(fmt.Sprintf("%s$%s", sep, envVal))
 			sep = " "
 		}

options.go

@@ -256,15 +256,15 @@ func (o *opt) String() string {
 }
 
 func mkOptStrs(optName string) []string {
-	namesSl := strings.Split(optName, " ")
-	for i, name := range namesSl {
+	res := strings.Fields(optName)
+	for i, name := range res {
 		prefix := "-"
 		if len(name) > 1 {
 			prefix = "--"
 		}
-		namesSl[i] = prefix + name
+		res[i] = prefix + name
 	}
-	return namesSl
+	return res
 }
 
 func (c *Cmd) mkOpt(opt opt) {