Fix version constraints

Strongly-typed member variables

Update dependencies for 2.0

Fix method signatures #16

Merge pull request #15 from phpfui/PSRFixes

Update to new Psr\Http\Message\StreamInterface spec

Merge pull request #12 from phpfui/PHP71

Modernize to PHP 7.1

Merge pull request #10 from phpfui/PHP82

PHP 8.2 support

Merge pull request #9 from alexei-bykovski/fix-PHP-8.1-deprecation-no…

…tices

Fix PHP 8.1 return type deprecation notices.

Update guzzlehttp/psr7 version requirements

Library no longer compatible with versions less than 1.7

Remove travis.yml