Seperate _id and from its timestamp by adding a field created field.

This is so that on requeue or acksend when the id is reused the time is still updated.
Remove unneeded continue and cover more lines.
Add phpcs into build.
Use background for index creation.

This is the only way to create indexes safely while in running production.
make build.php executable
Merge pull request #13 from gaillard/master

_id and created fix, phpcs in build, background index, composer update