New features and bugfix

Alias for close function

Rewrite variables in camelCase.

Added hide() function and modified close() function as alias of hide().

Renamed "failure" to "error"; added "warning" status.

Modified "status" parameter for show() function: you can send "success"
/ "info" / "error" / "warning" string or `true` boolean (for "success")
and `false` boolean (for "error").

Added variable to prepend / append text to success / info / error /
warning message.

Fixed a bug that which assigned a class of error or success to an alert
already exists.