Added a CodecOptions() to context.Context and webcontext.Webcontext to allow codec options to be set on a context, then passed to a codec upon a call to WriteResponseObject.
Made docs for CodecOptions clearer and changed name of CodecOptions test to match other test names
Use a copy of the codec options so that the original isn't modified.
Revert "Use a copy of the codec options so that the original isn't modified."

Using a copy in conditional situations probably isn't a good idea, but always using a copy will allocate additional memory.  Reverting copy change and updating docs to explain that the value can be modified during a response.

This reverts commit eea6140dd6d66ae4c9ec2578fd9e95848eac7990.
Docs and avoid overwrite

Updated documentation to note that responders may add options to the CodecOptions map.  Updated the callback option code to ensure that it doesn't overwrite values that have been set previously.
Merge pull request #80 from stretchr/codec-options-passthrough

Codec options passthrough