rustup
Merge pull request #181 from hyperium/rustup

rustup
header: add If-Modified-Since support
Merge pull request #183 from cmr/if-modified-since

header: add If-Modified-Since support
Add missing reexport
Merge pull request #184 from cmr/if-modified-since

Add missing reexport
add etag header
Merge pull request #180 from wenderen/etag-header

add etag header