feat(index): Auto add closing keyword to commit

This commit allows users to correctly place and invoke the appropriate
keywords in the commit body so that it will autoclose intended issue(s).

The plugin can handle both no issues given and any delimited list of
issue numbers.

This commit also makes a small update to make body commit messages
optional.

index.js

@@ -65,7 +65,7 @@ module.exports = {
         type: 'input',
         name: 'body',
         message: dedent`
-          Give description of what changed and/or why:
+          Give description of what changed and/or why (optional):
         `
       }, {
         type: 'input',
@@ -77,7 +77,7 @@ module.exports = {
         type: 'input',
         name: 'issues',
         message: dedent`
-          List any issues closed by this change:
+          List any issue(s) closed by this change (e.g. 123, 124):
         `
       }
     ]).then(answers => {
@@ -100,6 +100,15 @@ module.exports = {
       // Wrap these lines at 72 characters
       const body = wrap(answers.body, wrapOptions);
 
+      // Auto-add closing keyword to commit message body
+      const issueNums = answers.issues.match(/(\d+)/g);
+      const issues = issueNums == null ?
+            null :
+            issueNums.map(function(x) { return "Closes #" + x; })
+                     .reduce(function(acc, val) {
+                         return acc + "\n" + val;
+                     }, "");
+
       // Apply breaking change prefix, removing it if already present
       let breaking = answers.breaking.trim();
       breaking = breaking ?
@@ -108,8 +117,6 @@ module.exports = {
 
       breaking = wrap(breaking, wrapOptions);
 
-      const issues = wrap(answers.issues, wrapOptions);
-
       // if no breaking or issues filter them out
       const footer = [ breaking, issues ].filter(Boolean).join(divider);
       commit([ head, body, footer ].join(divider));