Merge pull request #31 from a-warner/turn_off_server_tokens

Don't show server_tokens
Make target file name explicit
Include `STACK` environment variable in file name
Vendor binary for "cedar-14" stack
fix race condition
Merge pull request #35 from tt/support-cedar-14

Support "cedar-14"
Merge pull request #36 from yingted/master

fix race condition
Merge remote-tracking branch 'upstream/master'