Added scheme check in http client

3.0.2

added scheme check

Fixed requests with custom headers

The http client had a type in the options array for headers.

Updated to PHP 7.4 and PHPUnit 9

3.0

updated markdown syntax

Improved header parsing

Fixed \arc\http::getCacheControlTime()
Added support for multiple Cache-Control headers
Added \arc\http::parseHeader, parses headers with comma seperated values
Added \arc\http::mergeHeaders, merges one or more instances of headers with comma seperated values into one

Added HTTP header parsing, micro router, documentation

This release is slightly backwards incompatible. Specifically we renamed 'ClientInterface' to 'Client', as 'interface' is redundant.

arc-web: minor fixes, code style cleanup

fixed bug in \arc\http\ClientStream::headers, now removes trailing empty header
fixed coding style more to PSR-2