Load single fixture file (issue #36)

[ebarbeito]

Early implementation of requested feature Load single fixture file (issue #36). Main changes:

• The command line has a new --fixture-file option with a required value: one bundle fixture file that must be defined within khepin_yaml_fixtures.resources section. If not, it will throw an \Exception().
• Now YamlLoader::loadFixtures and YamlLoader::loadFixtureFiles may receive one extra argument (the reqiured value specified with --fixture-file option)
• Redefinition of YamlLoader::bundles class property just with the specified single bundle fixture file.

About the exception thrown if an unknown bundle fixture file is specified: I really don't know which is your best choice for that, but in my opinion when a user write a incorrect value for --fixture-file option, the execution shouldn't countinue. And an exception seems (for me) the best choice.

[khepin]

Hey, sorry for the delay it seems I missed a lot of GH notifications. Wouldn't a specific context be enough to solve your issue here?