chore(CHANGELOG): introduce perf() section for performance-related commits

Instead of using fix() or chore() when labelling a commit which improves
speed or performance use perf(). Perf commits will be listed in the
CHANGELOG under "Performance Improvements".

For example:
perf($animate): cache all getComputedStyle operations to reduce additional reflows

CONTRIBUTING.md

@@ -198,6 +198,7 @@ Must be one of the following:
 * **style**: Changes that do not affect the meaning of the code (white-space, formatting, missing
   semi-colons, etc)
 * **refactor**: A code change that neither fixes a bug or adds a feature
+* **perf**: A code change that improves performance
 * **test**: Adding missing tests
 * **chore**: Changes to the build process or auxiliary tools and libraries such as documentation
   generation

changelog.js

@@ -142,6 +142,7 @@ var writeChangelog = function(stream, commits, version) {
   var sections = {
     fix: {},
     feat: {},
+    perf: {},
     breaks: {}
   };
 
@@ -169,6 +170,7 @@ var writeChangelog = function(stream, commits, version) {
   stream.write(util.format(HEADER_TPL, version, version, currentDate()));
   printSection(stream, 'Bug Fixes', sections.fix);
   printSection(stream, 'Features', sections.feat);
+  printSection(stream, 'Performance Improvements', sections.perf);
   printSection(stream, 'Breaking Changes', sections.breaks, false);
 }
 
@@ -186,7 +188,7 @@ var getPreviousTag = function() {
 var generate = function(version, file) {
   getPreviousTag().then(function(tag) {
     console.log('Reading git log since', tag);
-    readGitLog('^fix|^feat|BREAKING', tag).then(function(commits) {
+    readGitLog('^fix|^feat|^perf|BREAKING', tag).then(function(commits) {
       console.log('Parsed', commits.length, 'commits');
       console.log('Generating changelog to', file || 'stdout', '(', version, ')');
       writeChangelog(file ? fs.createWriteStream(file) : process.stdout, commits, version);

validate-commit-msg.js

@@ -21,6 +21,7 @@ var TYPES = {
   docs: true,
   style: true,
   refactor: true,
+  perf: true,
   test: true,
   chore: true,
   revert: true