Update travis.yml

The head of the repo is CakePHP 2.3+ only. Also test against 5.4
Clone the whole cakephp tree.
Remove odd bash operator.
Add missing doc blocks + fix property.
Clear the filesList when generating assets.

This fixes issues with themed assets. Generating the same asset with
different themes would result in the first themed file being included in
all output files regardless of the theme.

Fixes #149
Add composer.json file.
Start adding filemtime to config objects.

The config file changing should also be involved in expiring build
files. Components in builds can be shuffled around without modifying the
component files. This situation should trigger build refreshes.
Make isFresh() return false when the config file has changed.

If the config file has changed since a build was created, builds should
not be considered fresh. Config changes can dramatically alter the
output files without the contents of any other file changing.
Make code comply with CakePHP's coding standards
Merge pull request #153 from ataylor32/coding-standards

Make code comply with CakePHP's coding standards
Aside from the base asset_compress.ini all loaded plugins are scanned for asset_compress.ini files. When found they are applied  to the config instance
Detect plugin asset files