Some documentation generation fixes

- Add docgen command to use internal libraries
- Fix loading of base files due to plugin path changes
- Fix loading of jar dependency files
- Remove kramdown gem and actions
- Cleanup the generated synopsis a bit

Fixes #2009
added rake vendor:force:gems option for forcing a bundle install

Fixes #1952
Use returns instead of exit

Need to return the exit code and let the runner app perform the exit

Fixes #1838
Only print 'relaunching' if run under debug.

Fixes #1995
Fix tarball packaging to be rooted in logstash-<VERSION>

Fixes #1982

Fixes #1995
Remove some vendor tasks from vendor:all

kafka, geoip, elasticsearch, and collectd moved into separate plugins

Fixes #1995
bump ftw dependency to 0.0.40

Fixes #2000
Cleanup plugins to move to plugin system

Plugins have moved to https://github.com/logstash-plugins/... into
individual repositories. One plugin per repo.

* Add plugin install task and add required plugins for testing
* Adding a plugin task to install plugins
* Added required plugins to a prep task for the test part.

Fixes #1984
Add missing rubysl (rubinius libs) support.

This was already present in 1.x and 1.5 branches; not sure why master
was missing it.
Wrapper for bin/logstash plugin Closes #1969

Fixes #2017
Fixed usage comments

Fixes #2017
Use exec instead of sourcing

Fixes #2017
Fix typo in install

Fixes #2019
Add init scripts to rpm and deb

Fixes #2018
Adding option to download remote files as part of the gem

- Adding minitar as dependency
- Adding vendor file to handle the tasks
- Adding vendor hook to install and update actions

the vendor.json file should be placed at the root of the gem file
This file defines all the remote sources that should be downloaded.
The content of it is an array of hashes.
Each hash has the following settings:
- url
- sha1
- files

url is the url of the remote source
sha1 is the sha1 fingerprint we use for validation of the downloaded file
files can have different settings and is only used for .tar.gz / .tgz files
not setting it extracts the whole tar.gz file
An array of files allows to extract specific files
A Regexp allows extracting specific files

Fixes #2029
Move most common functions away into a util method

Fixes #2029
Update after review

Fixes #2029
Update License

Fixes #2030
Fix asciidoc formatting of the base config options

Fixes #2035
Fix asciidoc link to string reference

Fixes #2038