Merge pull request #1 from alexcrichton/updates

Update to master and implement get_header()
Change to_c_repr() to with_c_repr()

This prevents a use-after-free in curl when passing C strings to curl.
First full-stack test
Expose response headers and cleanup some warnings
Merge remote-tracking branch 'alex/with_c_repr'
Return builder from get(...) and post(...) fns
Support reusing curl handles
Minor README update
Fix an error in README
Basic support for POST bodies
HTTP POST with Reader as body
Cleanup tests
Test keep alive requests with various methods
Add support for HEAD requests
Lower case header names
Cleanup warnings
Expand curl version info support
Finish cleaning up warnings
test: Use new byte literals instead of macros
Run the curl cleanup function at process exit

This helps to cut down on the leaks when the process exits.