inline_caching, a fix for has_one, and automatic ancestor id params

Hey guys!

I'm switching from active-resource to her in my company. During this switch (isn't completed yet) I made some additions to the gem. I hope you like it and will integrate into the main gem.

Inline Caching:
We are going to integrate with an external cache system and looked for a way to better control caching inside of Her. With "disable_inline_caching" the inline caching functionality can be controlled on a per model basis.

Has One Fix:
This is a little fix to allow the has_one association to allow custom primary_keys on build.

Ancestors:
Since we are building complex internal API's with many levels of nesting. I created a way to better handling automatic id lookup's when building on a nested collection.

Tell me what you think about these additions!