TASK: Rename primary composer plugin type

Closes #24

See merge request !24

TASK: Remove travis-ci configuration

Closes #26

See merge request !23

Readded old composer package type `php-codesniffer-standards`.
Will be removed before the first stable release.

Added `phpcodesniffer-standards` (plural) as also supported
composer package type.

As requests in #24 i renamed the primary composer plugin type
from `php-codesniffer-standards` to `phpcodesniffer-standard`
for compatibility reasons to other projects.

Resolves #26

Feature/17 write status messages to stdout

Bugfix/18 installer is installed seems not to work

Feature/13 php54 requirements error

Feature/11 integrate phpunit

Feature/5 integrate travis ci

Resolves #3

Resolves #2

Resolves #1