Implement skip cache by URI path & response header

[ooaklee]

Motivation

Firstly, this is a great package - thank you. I found that in the use case where someone might have wanted to skip caching particular responses or server paths intentionally, they were previously limited. With these proposed changes, users can specify a regex to restrict the cache's scope or set a previously defined header in their handler function to ensure the response is never cached (suitable for partially loaded site set-up, amongst other use cases).

What's Changed

• Added a new ClientOption that takes the name of the response header used to skip caching response
• Added a new ClientOption to allow a user to specify a URI path regex that skips caching for matching requests.
• Updated README