Note PHP 5.2+ support in the README

Fixes #51
Add ability to get all headers as an array

Fixes #8
Use relative links in documentation
Handle serialization/deserialization ourselves

cURL can't be trusted to do this, since it doesn't deal with nested arrays.

Fixes #35, see #33
s/flattern/flatten/ Props @joncave
Skip cURL tests if cURL is not enabled
Make compatible_gzinflate() and decompress() public
Be a little more sensible with gzinflate
Add advanced gzip decoding thanks to @dd32

This is based on source code from WordPress.com by @dd32 based on their
usage patterns.
Store headers internally as arrays and refactor

This lets us do more magical stuff in other places, since we might need
case-insensitive dictionaries elsewhere. The internal use of arrays
breaks one test at the moment, this will need to be fixed.
First pass at cookie support

Still needs tests.
Trim all cookie keys and values
Add initial proxy support
Use a class for proxy support
Update example for authentication
Add documentation on using proxies
Readme fix related to PSR-0 class loader
Merge pull request #71 from fulopattila122/master

Readme fix related to PSR-0 class loader
Merge pull request #70 from rmccue/proxy

Add full proxy support, major props @ozh
Ensure casting a cookie to a string uses the value