(fix) Harden header parsing against memory exhaustion attacks.

Adds new limits on the lengths of header names and fields.

Fixes #187
fix(ssl): set_hostname on ssl connections
Merge pull request #191 from reem/max-header-lengths

(fix) Harden header parsing against memory exhaustion attacks.
Merge pull request #192 from hyperium/ssl-set-hostname

fix(ssl): set_hostname on ssl connections
add vary header, first draft
rust upgrade
Merge pull request #195 from hyperium/rustup

rust upgrade
Merge pull request #193 from wenderen/vary-header

add vary header, first draft