Fix kafka installation on Opsworks

Chef's file cache path is apparently only readable by `root` on
OpsWorks, so we have to extract the release archive as root and then
manually set ownership.
Merge branch 'pfleidi-fix-opsworks-file-cache-permissions'
Account for different ways of defining `log.dirs`

The (obvious) downside of having too many ways of defining configuration
attributes. Perhaps I’ll revise that decision in the future, but for now
it’s not too much of a hassle.
Version bump to v0.5.0

Quite a “large” release with a ton of changes, ranging from a rewrite of
how “configuration attributes” are managed to minor fixups:

* Removal of `zookeeper` recipe. Use a dedicated cookbook for that.
* Host all “configuration attributes” under a `broker` namespace.
* Configurable and sane log4j properties (see `attributes/default.rb`
  for examples).
* Configurable KAFKA_GC_LOG_OPTS environment variable through the
  `gc_log_opts` attribute.
* Bugfix for using this cookbook with AWS OpsWorks (thanks to @pfleidi).
Fix incorrect attribute syntax in README

[ci skip]
Rewrite `recipes` intro. in README

[ci skip]
Remove unnecessary comment from default attributes
Remove unnecessary `log_dirs` attribute
Set defaults in a separate (private) recipe

Since one can define broker configuration options in a number of
different ways we cannot really set broker defaults in an attributes
file.

Instead we set them in a `_defaults` recipe, but only if they aren’t
already set to something, as we don’t want to override what a user has
already set.

Closes #55.
Version bump to v0.5.1

Bug fix release with a fix for #55.
Use SVG badge for build status

[ci skip]