Allow to scope entries by request attributes.

Adds a public_entry_request_scope configuration setting which allows
restricting the avaiable published entries under a specific host. For
example, the entries accessible under an account's CNAME can be
restricted to those of the account.
Merge pull request #61 from tf/request-scope

Allow to Scope Entries by Request Attributes #61

Adds a public_entry_request_scope configuration setting which allows
restricting the avaiable published entries under a specific host. For
example, the entries accessible under an account's CNAME can be
restricted to those of the account.

Conflicts:
	CHANGELOG.md