Add handlers to README.md
New Handler for Pushover.net

- composer.json suggest: linkorb/pushover
- includes unittest, reads config from environment
- support recipient info 'pushover.user_key'
Merge pull request #8 from linkorb/handler-pushover

New Handler for Pushover.net
Apply coding standards and improve tests.
Add PushoverHandler handler to README.md
Add config placeholders in phpunit.xml.dist
Update gitignore
Prevent test from failing if Github API limit problem occurs.
https://github.com/composer/composer/issues/1314
Update installation.md
Merge remote-tracking branch 'nousefreak/master'

Conflicts:
	composer.json
add test script