Tweak the travis-ci badge and add a github issues badge.
Code quality enhancements for the Addons class.

- Add and fix some doc comments.
- Fix some bugs caused by mismatched visibility.
Fix some code quality issues in the Application class.

- Add some doc comments.
- Fix some object comparisons.
- Fix some return path issues.
Remove the Cli classes.

Cli functionality is now maintained in a separate repo at https://github.com/vanilla/garden-cli.
Fix some doc comments and dead code in the Event class.
Fix some issues in the Config class.

- Add some doc comments.
- Fix bug where Config::defaultPath() does not return a value.
Allow Route->methods() to take a string.
Core functions tweaks.

- Use the parameters from array_column_php() rather than the parameters from func_get_args().
- Remove some unused code.
Add support for $allow_slugs in is_id().
Remove unused variables in DjangoPassword.
Remove leftover itoa64 arguments in PhpbbPassword.
Fix missing result in XenforoPassword->splitHash().
Fix regression bug in XenforoPassword.
Add some doc comments to the Request class.
Fix some scrutinizer issues in the Response class.
Route class fixes.

- Fix typo where $this->mapping should be $this->mappings.
- Fill in the missing implementation of Route->mappedData().
Fix some scrutinizer issues in the Schema class and fill in some doc comments.
Fill in some doc comments for the Validation class.
Throw an exception in SecureString->hmac() if there is an error in hash_hmac().