Support .yaml file extension

[vkorobkov]

YML files have two valid possible extensions: .yml and .yaml

Currently we do not support .yaml extension and we need to fix it before the public release.

1. com.github.vkorobkov.jfixtures.config.ConfigLoader
   Should lookup for .conf.yaml first, in case of failure should lookup fpr .conf.yml

2. com.github.vkorobkov.jfixtures.loader.FixturesLoader#isYml should be fixed:

.endsWith(".yml") || .endsWith(".yaml")

There is an edge case here: if the same fixture exists with both extensions(like users.yaml and users.yml we need to throw an exception with a readable message)

[rodionovsasha]

PR #85

[rodionovsasha]

merged to master as 1.0.2.6. release