Allow to override excerpt words

In thinking-sphinx 2 one could easily override the excerpt words like that:

```
excerpt_options => {:words => "mywords"}
```

Would be nice if that was supported in thinking-sphinx 3 too:

```
excerpts => {:words => "mywords"}
```
Option to override excerpters words belongs to excerpter
Option to override excerpters words
Merge pull request #551 from groe/patch-1

Allow to override excerpt words
Spec to test :classes option across multiple models.
Add respond_to? method definition for search panes
Update riddle dependency to current edge
Respect :limit option on FacetSearch
Merge pull request #557 from epidemian/facets-limit

Respect :limit option on FacetSearch
Merge remote-tracking branch 'groe/patch-2'
method_missing on Glaze is private again, plus specs for respond_to?

Also, it's worth noting that calling 'super' in respond_to? will fire method_missing anyway, as there's no underlying implementation in a BasicObject instance. A little confusing, but that's just the way life is.
Clear task removes all Sphinx index and binlog files.
Making sure index location exists when starting daemon.

This matters for real-time indices, when there's no preceding index call.
Regenerate task for rebuilding Sphinx setup with realtime indices.
HISTORY updates.
Updating Riddle dependency to >= 1.5.7.
3.0.4
sphinx.yml has been renamed to thinking_sphinx.yml
Merge pull request #565 from steveyken/master

sphinx.yml has been renamed to thinking_sphinx.yml
Adding a test of chaining non-query scopes.