Allow bundle to be used without clients or indexes defined.
Move type configuration into independent method
Refactor documentation
fix some block comment
Make fetchSlice compatible with custom repo method

If a user configures query_builder_method for the doctrine provider, and
does not alias the root entity to equal Provider::ENTITY_ALIAS then a
DQL error will occur during index population.

> [Semantical Error] [...] near 'a.id ASC': Error: 'a' is not defined.

Provider::countObjects already handles this by dynamically fetching the
alias with QueryBuilder::getRootAliases, and Provider::fetchSlice should
be doing the same.

nb. "Provider" refers to FOS\ElasticaBundle\Doctrine\ORM\Provider
Unset fields if no nested fields are defined
Merge pull request #514 from jvandesande/MultiField

Unset fields if no nested fields are defined
Merge pull request #505 from piotrantosik/fix_docblocks

Fix some block comment
Merge branch 'master' into documentation

Conflicts:
	DependencyInjection/Configuration.php
	README.md
Merge pull request #510 from peterjmit/master

Make fetchSlice compatible with custom repo method
Documentation updates
Merge pull request #435 from merk/documentation

Refactored documentation
Logger enabled with debugging
Update changelog
Update logger documentation based on configuration change
Merge pull request #519 from merk/logger-debug

Change logging to only be enabled in debug mode
Corrected bundle class name in install instructions
Merge pull request #521 from morticue/master

Corrected bundle class name in install instructions
Unset nested "fields" for deeper nested configs too
Upsert-type functionality for existing ORM Entities

This is an attempt to fix the issue: https://github.com/FriendsOfSymfony/FOSElasticaBundle/issues/526

It will cause a significant slowdown in a large batch, but it appears to be the only way to prevent an exception from bubbling up during a normal use case.