Set Headers now iterates over key

The NameValueCollection iterator returns the string key, not a
KeyValuePair.
Tabs -> spaces per cefsharp guidelines.

Tabs -> spaces per cefsharp guidelines.
NameValueCollection allows for duplicate keys.

For each key get each of the values that matches the key.
Merge pull request #413 from rlmcneary2/master

Set Headers now iterates over key