Purify buildRequest function
Merge branch 'master' into wip/pure-request-builder

Conflicts:
	http-common.cabal
Correct indentation in example
Merge branch 'pure-request-builder'

Closes https://github.com/afcowie/http-streams/issues/9
Closes https://github.com/afcowie/http-streams/pull/62
Closes https://github.com/afcowie/http-common/pull/9
Closes https://github.com/afcowie/http-common/pull/11