Added make request code that will take care of expire and cache

We should probably think about parallel locks and stuff but ill look
more into it. Alex will update the code for
getValidCachedResponse to return response. Right now, it fails 2 of the
4 tests because getValidCachedResponse is not complete
Merge branch 'master' of https://github.com/sumo2478/CS118

Conflicts:
	cs118-project1/http-proxy.cc