Use of a virtual file system on tests to prevent having untracked files
Merge pull request #87 from aaa2000/phpunit-untracked-files

Use of a virtual file system on tests to prevent having untracked files
Removes guzzle dependency.
Removes guzzle client usage in HttpClient.
Rewrites request and response to not use guzzle.
Fixes double >.
Stores status message and http version in Response if available.
Extracts HTTP parsing related methods to HttpUtil.
Forwards HTTP status as header to Guzzle.
Adds request error status code.
Adds guzzle version 3 integration test.
Fixes tests.
Refactors guzzle version 3 tests.
Adds guzzle version 4 tests and fixes.
Adapts travis configuration to run guzzle 3 and 4 tests.
Trying to remove PHP language.
Trying to add php versions to matrix.include.
Fixes Response toArray test.
Readds env variables.
Adds `composer install` for library dependencies.